History of the incandescent lamp

NORTHEASTERN UNIVERSITY
LIBRARIES

Presented by
Mr. Raymond Ayer

HISTORY OF

THE INCANDESCENT

LAMP

JOHN wl HOWELL

AND

HENRY SCHROEDER

THE MAQUA COMPANY, Publishers

SCHENECTADY, NEW YORK

1927

Copyright, 1927, by
The Maqua Company

Printed in the
United States ot America

Published 1927

CONTENTS

PAGE

Introduction 4

Chapter One — Development of Electric Lighting

Prior to Edison's Invention 7

Chapter Two — Edison's Invention of a Practical In-
candescent Lamp, a Complete Lighting System
and Their Commercial Introduction ... 45

Chapter Three — Development of Filaments . . 75

Chapter Four — The Vacuum, "Getters" and the

Gas Filled Lamp

Chapter Five — Leading-in Wire Developments
Chapter Six — Glass Construction
Chapter Seven — The Base ....
Chapter Eight — Photometr}^
— Index ........

123
155
163
182
193
206

3/2 2 3

i

INTRODUCTION

The Incandescent Electric Lamp as made and patented
by Mr. Edison, is the foundation stone upon which
the great electric light and power industry of to-
day has been built. The great electric companies which
were organized in the early 80's, — the Edison Electric
Illuminating Companies, as they were generally known, in
New York, Boston, Philadelphia, Chicago and in many
other places — were organized to light their territories with
the Edison incandescent lamp. This was practically the
only business or source of revenue that these companies had,
since electric motors were not well developed and came
slowly into use.

When Mr. Edison started to make a lamp factory at
Menlo Park, in the fall of 1880, he started an entirely
new industry. He could get no tools, machinery, or ex-
perience from other industries, therefore they all had to be
created, designed, and built from experience as he went along.
Lamps were still more or less of a mystery, and the simple
laws relating to them were not well understood. Electrical
instruments were home made, as no suitable ones could be
purchased. The Harrison lamp factory was wired with
bare wire, stapled on the wood beams, and no cut-outs or
switches were available. An Archimedes screw pump for
raising the mercury used in exhausting lamps was the only
piece of machinery used in the Menlo Park lamp factory,
except the blower used by the glass blowers and in the
carbonizing room.

Constant experimenting was done to determine the
relative advantages of different ways of performing the
various operations, and it was a long time before definite
methods were settled upon. These methods were frequently
changed as more experience was accumulated.

Many lamps were burned on life test from the very
beginning, to determine the relative value of the various
experiments. This constant experimenting and testing
made the work most interesting.

During the first 3^ear or two, Mr. Edison spent a good
deal of time at the factory, and had a laboratory there.
His presence and leadership were a great inspiration to all,
so that time meant nothing to those who were helping him
to carry out his work or experiments.

As the various methods of manufacture became settled,
it became possible to organize the factor\^ operations and to
adopt piece work methods; but it was a long time before
any lamp making machinery enabled the substitution of un-
skilled labor for the skilled glass workers. It is hard for
anyone who sees the modern lamp factory to realize the
work done in developing the art to its present degree of
perfection.

The lamp is apparently very simple, but its design,
manufacture, and development require quite a broad knowl-
edge of physics and chemistry. This has attracted many
bright-minded men to the industry, who have found it a
most interesting field of work.

The growth of the business, from the invention of the
lamp to the present day, has all taken place during the
working lives of some of the men still in the business.
This history of the lamp has been written in order to
portray the changes and developments which brought it
to its present high state of perfection and efficiency.

John W. Howell
Henry Schroeder
March, 25, 1927.

CHAPTER ONE

Development of Electric Lighting Prior to
Edison's Invention

The word electricit}^ originates from the Greek name
for amber, "elektron;" Thales, a Greek philosopher having
recorded the fact about twenty-five centuries ago that if
amber is rubbed it will attract objects of light weight. About
two hundred and fifty years later Aristotle, another Greek
philosopher, found that a mineral, later called lodestone
and now known to be the iron ore magnetite, would attract
iron. The word magnet comes from the fact that lode-
stones were first found near Magnesia, a city in Asia
Minor. The word lodestone, an abbreviation for "leading
stone," comes from the fact, probably discovered by
sailors in the northern countries of Europe, although it
has been often credited to the Chinese, that this mineral
would point to the north if suspended like a compass.

William Gilbert, physician to Queen Elizabeth of Eng-
land, made a ntimber of experiments, among which was
the discovery of magnetic lines of force, and of north
and south poles in a magnet. He wrote a book about the
year 1600 summarizing the then known facts about elec-
tricity and magnetism. A few years previously Robert Nor-
man had discovered that the amount of dip of the compass
needle varied at different points on the sphere. From this
he deduced that the earth was a magnet and assumed
that the magnetic and geographic north poles were the
same. It has since been found that these poles do not
coincide. Gilbert also discovered that many substances
beside amber would also attract light objects if rubbed.

Otto Von Guericke, about 1650, made a machine con-
sisting of a ball of sulphur mounted on a shaft which could
be rotated. Electricity was generated when the shaft was

THE INCANDESCENT LAMP

rotated and the hand lightly pressed against the rotating
sulphur ball. He also discovered that the electricity
generated could be conducted away from the sulphur
ball by a metal chain from which sparks could be obtained.
Francis Hawksbee, about sixty years later, made a similar
machine, using a hollow glass globe from which the air
had been exhausted by the vacuum pump that had been

OTTO VOi\ GUERICKE'S ELECTRIC MACHINE. 1G5{).
Electricity was generated by friction between the hand and the rotating
sulphur ball.

invented by Von Guericke. This exhausted globe when
rotated at high speed and rubbed against the hand pro-
duced a glow of Hght. This electric Hght, as it was called,
created a great excitement when it was shown before the
Royal Society, a gathering of English scientists. Those
machines were forerunners of the frictional glass disc
machines which generate electricity at very high pressures

THE INCANDESCENT LAMP

(but in very small quantities) so that long sparks can be
produced. They are now occasionally used for medical
purposes.

Stephen Gray, about 1729, demonstrated before the
Royal Society that electricity could be conducted about
a thousand feet by a hemp thread. This was possible if
the hemp thread was supported by silk thread but
could not be done if metal supports were used. Charles
duFay, in 1733, showed that those substances, which Gilbert
had found could be electrified if rubbed, were insulators;
and those substances which could not be electrified were
conductors of electricity.

Von Kleist, about 1745, invented the so-called Leyden
jar, the forerunner of the present condenser, in attempting
to store electricity. The name came from the fact that it
was independently discovered shortly afterward by experi-
menters in the University of Leyden. Von Kleist, knowing
that the frictional machines generated so small a quantity
of electricity, thought he could store it in a glass bottle
full of water, as water was known to be a conductor and
glass an insulator. In the bottle was a cork with a nail
through it, the nail touching the water inside. Holding
the bottle in one hand and turning a frictional machine
with the other, the machine being connected to the nail
in the cork, he proceeded to fill the bottle with electricity.
After turning the machine for a few moments he pulled the
bottle away from it and then touched the nail with his
hand. The shock threw him down and nearly stunned
him. Later it was found that the hand holding the bottle
was as essential as the water inside, both being later re-
placed by tin foil.

Benjamin Franklin made numerous experiments with
the Leyden jar. He connected several jars in parallel
and produced a discharge strong enough to kill a fowl.
He also connected jars in series (in "cascade" he called
it), thereby establishing the principle of parallel and series
connections. Franklin's most famous experiment is his
proof that lightning is electricity. This he did in 1752, by

THE INCANDESCENT LAMP

flying a kite in a thunderstorm, and drawing electricity from
the clouds with which he charged Leyden jars and drew
sparks from a key attached to the kite string. It is a
wonder that he was not killed by this experiment. These
experiments led to his invention of the lightning rod.

VOLTAIC PILE," 1799
Volta discovered the principle of the present day primary battery,
one form of which is the so-called dry battery used for flashlights and
in radio. This was the first time that electricity could be obtained in
considerable quantity and the. VOLT is named after him in honor of
this discovery. Photograph, courtesy of Charles F. Chandler
Museum, Columbia University, New York.

Volta' s Invention of the Primary Battery

About 1785, so it is said, the wife of Luigi Galvani, an
Italian scientist, was in delicate health. Some frogs' legs
were being skinned to make her a nourishing soup. Gal-
vani's assistant, holding the legs with a metal clamp and
cutting the skin with a scalpel, happened to let the clamp

10

THE INCANDESCENT LAMP

and scalpel touch each other. To his amazement the frogs'
legs twitched. Galvani repeated the experiment and pro-
posed a theory of animal electricit}^ in a paper he pubHshed
in 1791.

Allesandro Volta, a professor of physics at the Univer-
sity of Pa via in Italy, repeated Galvani 's experiments and
found that the clamp and scalpel must be of different
metals. He beHeved that the electric charge which made
the muscles in the frogs' legs convulse was caused by
the action of the moisture in the muscles on the different
metals. Following up this idea, he made a pile of silver
and zinc discs, probably coins, with pieces of cloth wet
with salt water between them. From this Voltaic Pile, as
it was called, he found that electricity could be obtained.
In March, 1800, he sent a letter to the Royal Society in
London, describing his invention, and the volt, the unit
of electrical pressure, was named after him in honor of this
discovery.

It was later shown that the chemical affinity of one
of the metals for the liquid was converted into electrical
energy. In Volta 's Pile the zinc combines chemically with
the salt water when a wire is connected to the silver and
zinc terminals, forming zinc chloride, caustic soda and
hydrogen gas.

A more powerful battery was made by the use of copper,
zinc and dilute sulphuric acid. The zinc combining with
the sulphuric acid forms zinc sulphate and hydrogen gas.
The latter appears as bubbles on the copper plate and
reduces the voltage of the battery, this being called "polari-
zation." Minute impurities in the zinc will cause the zinc
to be attacked even when the circuit is open, as the im-
purities form a local short circuited cell. This is called
"local action," and in order to prevent the zinc from being
uselessly consumed, it was removed from the dilute acid
when the battery was not in use. Later it was found that
this difficulty could be largely overcome if the zinc electrode
were rubbed with a little mercury, so that its surface
became amalgamated.

11

THE INCANDESCENT LAMP

Improvements in Batteries

The main difficulty with the copper-zinc-sulphuric
acid battery was the formation of hydrogen gas bubbles on
the copper electrode (polarization) which greatly reduced its
operating voltage, and it was found that if the bubbles
were removed, by brushing them off with a stick of wood
for instance, the capacity of the battery would be greatly
increased.

In 1836, John Frederic Daniell, an English chemist,
invented a chemical means of overcoming this difficulty.
He made a battery consisting of an amalgamated zinc rod
in dilute sulphuric acid, as in the previous batteries. These
were placed in a porous earthenware jar which was put in a
saturated solution of copper sulphate. Thus the dilute
sulphuric acid was kept ph^'sically separate from the copper
sulphate solution, but the two liquids were in electrical
contact with each other through the pores of the porous
cup.

The other electrode was copper and was immersed in
the copper sulphate solution. The chemical action of the
battery was that the zinc combining with the sulphuric acid
formed zinc sulphate and h^^drogen gas as before. The
hydrogen gas going through the pores of the cup combined
with the copper sulphate, forming sulphuric acid and
metallic copper, the latter being deposited on the copper
electrode. Crystals of copper sulphate were kept in the
copper sulphate solution to maintain it in a saturated
condition. Later the porous cup was dispensed with, the
two solutions being kept apart by their difference in
specific gravity. This was called the gravity battery, and
for many years was used in telegraphy. The voltage of
this battery was about one volt per cell.

Sir William Robert Grove made a notable further
improvement in batteries. It was known that the electrical
energy of the zinc-sulphuric acid cell came from the chemical
affinit}^ of the two, and that if the hydrogen gas set free could
be combined with oxygen to form water, such additional
chemical affinity would increase the strength of the cell.

12

THE INCANDESCENT LAMP

Nitric acid was known to be a very active oxidizing agent,
but as it attacks copper, platinum was sub^ituted as the
material for the positive electrode, where the hydrogen gas
bubbles appear.

In 1840 Sir Robert made a battery consisting of a plat-
inum electrode in strong nitric acid which was kept in the
inner porous jar to prevent it from attacking the zinc elec-
trode. This combination was put in dilute sulphuric acid
containing the amalgamated zinc rod electrode. The hydro-
gen gas, liberated by the action of the sulphuric acid on the
zinc, combined with the nitric acid to form nitrous peroxide
and water. Part of the nitrous peroxide dissolved in the
water and the rest escaped in the form of very suffocating
fumes. This battery had almost double the strength of
previous batteries, having a voltage of about 1.9 volts.

Some years later Grenet improved the battery by
substituting a solution of potassium bichromate for the
nitric acid. This solution could be mixed directly with
the sulphuric acid, as it does not attack zinc to a great
extent. The porous jar was, therefore, unnecessary and
no fumes were formed. To lessen the cost, a slab of carbon
was used for the positive electrode. The zinc electrode was
fastened to a sHding rod so that it could be drawn up
into the neck of the bottle shaped jar containing the liquid,
to prevent the useless consumption of zinc when the bat-
tery was not in use.

The Ampere

Andre Marie Ampere was a professor of mathematics
in the Polytechnic School in Paris. In 1820 Oersted, a
professor of physics in the University of Copenhagen in
Denmark, had announced his accidental discovery that
current flowing in a wire would deflect a compass from
its true position. Ampere repeated Oersted's experiments
and made a number of others from which he developed
several fundamental laws regarding current flowing in a
wire. He also discovered that current flowing in a coil of
wire gave it the properties of a magnet, and thus established

13

THE INCANDESCENT LAMP

the long sought connection between electricity and mag-
netism. The AMPERE, the unit of flow of electric cur-
rent, was named for him in honor of his discoveries.
Ohm's Law

About the most important fimdamental law of electricity
was discovered in 1825, by Georg Simon Ohm, a teacher in
the High School in Cologne. It was known that the rate
of transfer of heat from one end of a metal bar to the
other was in proportion to the difference in temperature
between the ends. By analogy and experiment. Ohm
found that the current in a wire is proportional to the
difference of voltage (electric pressure) between the ends
of the wire. He also showed that the current in the wire is
inversely proportional to the electrical resistance of the wire.
With these as a basis. Ohm propounded the law that the
current flowing in a circuit is equal to the voltage divided
by the resistance. In honor of this discovery, the ohm, the
unit of electrical resistance, was named after him.

As often happens in such cases, critics derided this law,
and in this case the criticism was so severe that Ohm was
forced out of his position in the High School. Having
been born of parents in poor circumstances, and worked his
way through college in order to obtain an education, he
keenly felt the criticism which forced him to give up the
sort of work for which he had so earnestly striven. He
went back to his parents and worked in his father's black-
smith shop for over ten years. Finally he began to find
supporters to his theory and in 1841 his law was publicly
recognized by the Royal Society in London, which pre-
sented him with the Copley medal.

This simple law is at first difficult to understand, but
if once mastered will solve many electrical problems. It
is usually expressed as:

C = -

"C" meaning Current (in amperes)
"E" meaning Electromotive Force (in volts)
"R" meaning Resistance (in ohms)

14

THE INCANDESCENT LAMP

If two of the factors in the above formula are known,
the third can be readily determined. For example, an
incandescent lamp, burning on a circuit whose voltage
(pressure) is known to be 120, is found to consume Yi an
ampere of current. The electrical resistance of such a lamp
is therefore 240 ohms.

Perhaps the simplest analogy to an electrical circuit is
a hydraulic S3^stem. The voltage in an electrical system
is similar to the pounds per square inch pressure in the
hydraulic system. The amperes flowing in an electric
circuit are similar to the gallons per minute of water flowing
in a pipe; it is the rate of flow, not the actual volume. This
is often the stumbHng block to the uninitiated. Another
term similar to the ampere is rate of speed, which is usually
expressed in miles per hour. The difference between a rate
and an actual volume may be shown, for example, by the
size of an automobile storage battery which is expressed
in ampere-hours; that is, a 120 ampere-hour battery is
one which has the capacity to deliver 15 amperes continu-
ously for eight hours. vSimilarly a 120 gallon tank will deliver
15 gallons of water per minute for eight mintites; or an
automobile traveHng fifteen miles per hour will take eight
hours to cover 120 miles.

The resistance of an electrical circuit is generally
quite easy to understand. It is similar to the friction that
water encounters in flowing through a pipe. A large pipe
will allow water to flow through it quite easily, and there-
fore, has a low resistance in the same sense that a large wire
has a low electric resistance.

The Invention of the Dynamo

Schweigger, famihar with Oersted's and Ampere's
discoveries, invented the galvanometer (or "multiplier"
as he called it) which consists of a compass needle sus-
pended within a coil of wire. Current flowing in the coil
deflects the needle, the amount of deflection indicating the
strength of the current. This made available a very sensi-
tive electrical measuring instriiment.

15

THE INCANDESCENT LAMP

Sturgeon had also shown that if a bar of iron were
placed in a coil of wire the magnetic strength of the coil
would be greatly increased. This he called an electro-
magnet.

FARADAY'S DYNAMO. 1831
Michael Faraday invented the dynamo, the foundation of the elec-
tric light and power industry. The dynamo, however, did not
become commercially practicable until about forty years later.

Michael Faraday, born of EngHsh parents in poor cir-
cumstances, became a bookbinder and so was enabled to
study books on electricity and chemistry. His desire to
become a scientist was so great that he finally induced Sir
Humphry Davy to give him a position as his laboratory
assistant. He aided Davy in his lectures and experiments and
also made a number of experiments himself. As a result of
his own research work, he was elected to a Fellowship
in the Royal Society in 1824.

16

THE INCANDESCENT LAMP

Faraday then began a number of electrical experiments
in an endeavor to find further relation between electricity
and magnetism. Ampere having converted electricity into
magnetism, Faraday tried to find out if the reverse were
possible. Finally, in the latter part of 1831, he made the
experiment of moving a permanent magnet in and out of
a coil of wire connected to a galvanometer. This generated
electricity in the coil and the galvanometer needle was
deflected. He then made a machine consisting of a copper
disc mounted on a shaft so that the disc could be rotated
between the poles of a permanent horseshoe magnet. A
copper brush rubbed against the edge of the disc as it
rotated. A galvanometer was connected by wires to this
brush and to the shaft so that when the disc was rotated
by hand, the current generated deflected the galvanometer
needle.

Faraday, being satisfied with pure research work, did
not develop his discovery any further, so that it remained
for others to make it practicable. It was not, however,
until many years later that the dynamo became commercial,
and as it is the foundation of the electric light industry,
its development is of great importance.

The next year, 1832, Hippolyte Pixii, a Frenchman,
going back to Faraday's original experiment of moving a
permanent magnet in the neighborhood of a coil of wire,
and using Sturgeon's scheme of strengthening the mag-
netism in the coil of wire by a piece of iron, invented a
dynamo that was quite an advance over Faraday's disc
machine. It consisted of a permanent horseshoe magnet,
the ends of which were rotated about the ends of two coils
of wire mounted on a soft iron core. A commutator
changed the direction of the alternating current generated
so that direct current was obtained. This machine had
a very small capacity, about equal to that of the present
day standard dry cell used for an electric bell. It was
only a laboratory toy, but many of the principles of the
present day dynamos were embodied in it. Pixii obtained
a U.S. patent on his machine in 1832.

17

THE INCANDESCENT LAMP

In 1834, E. M. Clarke, an Englishman, made several
dynamos, the principles of which were the same as those of
Pixii's except that he rotated the coils of wire alongside the
poles of a stationary permanent horseshoe magnet.

PIXII'S DYNAMO. 1832
Hippclyte Pixii made a dynamo which was quite an advance. A per-
manent magnet rotated in the neiRhborhood of two coils of wire
mounted on an iron core, the alternating current generated being
rectified by a commutator. This is a photograph of the Patent
Office model which is on exhibition at the United States National
Museum, Washington, D. C, through whose courtesy the picture is
shown.

Pixii's and Clarke's dynamos produced a pulsating
direct current which was made unidirectional by means of
a commutator. While this means that they delivered direct

18

THE INCANDESCENT LAMP

current, their voltage (pressure) was pulsating. In 1841
Woolrich devised a machine which had several magnets
and double the number of coils, which reduced the piilsa-
tions. Wheatstone, in 1845, patented the use of electro-
magnets in place of permanent magnets. Brett, in 1848,

HJORTH'S DYNAMO, 1855
This may be called the first ' 'self-excited" machine, having permanent
magnet field poles inducing current in the armature which ener-
gized the electro-magnet fields. It was not used commercially.

suggested that the current given by a permanent magnet
machine be made to flow through coils surrounding the
permanent magnets to further strengthen them and
thereby increase the output of the machine.

About this time it was discovered that the iron sur-
rounded by the wire coils became heated due to currents
being generated in the iron itself while moving through the
magnetic field of the magnets. Such currents are called eddy

19

THE INCANDESCENT LAMP

currents, and in 1849 Pulvermacher proposed that the
iron be made into thin sheets to reduce them. All dynamos
now have a laminated sheet iron armature core.

In 1851, Sinstenden suggested that the current ob-
tained from a permanent magnet machine be used as a

SIEMENS' DYNAMO, 1856
Dr. Werner Siemens countersunk the armature wires in an iron
core, making a cylindrical shaped armature. This revolved between
magnet poles shaped to fit the armature, reducing the air gap and
so making a more powerful machine.

source of excitation to supply current to the field coils of an
electro-magnet machine. This scheme, though no permanent
magnet machines are now made, is generally used in all
large electric power stations, a separate machine being
used to supply current for the field coils of the large
dynamos.

20

THE INCANDESCENT LAMP

In 1855, Hjorth patented a dynamo having both per-
manent and electro-magnet field poles. The current, first
induced in the armature by the permanent magnets,
energized the electro -magnet field poles. This, therefore,
may be said to be the first "self -excited" electro-magnet
machine. It was not commercially used.

ALLIANCE DYNAMO. 1862

This machine was designed by NoUet for the commercial manufac-
ture of illuminating gas by decomposing water electrically. This
project failed, but in 1862 the machine was used to supply cur-
rent to the first commercial use of an electric light, an arc lamp in
the Dungeness Lighthouse in England.

Dr. Werner Siemens greatly improved the dynamo
by his invention, in 1856, of the shuttle wound armature.
The armature coil was countersunk in an iron core so as to
make a cylindrical armature which fitted closely between
the poles, which were shaped to enclose it. This greatly
reduced the air gap between the armature and field poles

21

THE INCANDESCENT LAMP

and thereby greatly increased the number of the magnetic
Hnes of force passing through the armature. This arrange-
ment, in principle, is used in all dynamos made today.

Another interesting dynamo is that designed in 1850, by
Nollet, a professor of physics at the Brussels Military
School. This dynamo had several rows of permanent

WHEATSTONE'S DYNAMO. 18(
This was the first self excited dynamo using the residual magnetism in
the field poles.

magnets mounted radially on a stationary frame, the
armature consisting of wire bobbins mounted on a shaft
which rotated within the frame. A commutator was used
so that direct current could be obtained. A company was
organized to supply hydrogen gas enriched with oils for
illuminating gas, the hydrogen gas to be made by the
decomposition of water with current from this machine.

Nollet died and the company failed. About ten years
later it was reorganized as the Alliance Company to exploit

22

THE INCANDESCENT LAMP

the arc lamp, which at that time (1860) had been fairly
well developed. Difficulties were experienced with the
commutator of the dynamo, so it was removed and col-
lector rings substituted, the machine then delivering alter-
nating current. A trial installation of the arc light was then
made in the Dungeness Lighthouse in England, the in-
stallation being formally accepted in 1862.

^'^•-1

GRAMME'S DYNAMO. 1871
Its mam feature was the "ring" wound armature. Several of these
machines were used in commercial service for arc lighting purposes.
This dynamo is in the historical collection of the Association of
Edison Illuminating Companies in conjunction with the Edison
Pioneers by whose courtesy this photograph is reproduced.

This was the first commercial installation of an electric
light, an arc lamp. The Alliance dynamo had a capacity
for one arc lamp, which probably consumed about ten
amperes at about 45 volts, and as the dynamo was very
inefficient, it probably required at least one and a half
horse power to drive it.

Sir Charles Wheatstone is credited with the invention
of the first self-excited machine which operated on
the principle of utilizing the residual magnetism in

23

THE INCANDESCENT LAMP

the field poles to set up a feeble current in
the armature, which, passing through the field coils,
gradually increases their strength until they are
built up to normal. He built a machine in the summer
of 1886, and exhibited it before the Royal Society at a
meeting held in February, 1867. A paper describing the
machine was read at this meeting. Another paper, for-

ALTENECK'S DYNAMO. 1872

The armature was "drum" wound, that is, the wires were wound on

the surface of the armature. This construction is used in all

dynamos made to this day.

warded by Dr. Werner Siemens, was also read at the same
meeting describing a similar machine invented by him.
Wheatstone probably preceded Siemens in this invention.
In 1870 Gramme, a Frenchman, made a dynamo having
a "ring" wound armature. The armature consisted of a
ring shaped core of iron wire which was coated with
an insulating compound to reduce the eddy currents.

24

THE INCANDESCENT LAMP

The core was wound with insulated copper wire
coils, all connected in series as one single endless coil, each
coil being tapped with a wire connected to a commutator
bar. The first machine built with electro-magnet fields
was made in 1871, and many of these were later built for
commercial arc lighting installations.

Alteneck, an engineer with Siemens, in 1872, invented
the "drum" wound armature. The wires were all on the
surface of the armature core, being tapped at frequent
points for connection with the commutator bars. This
meshod of construction is used in all dynamos now made.

=^mmmmmmm^

DE LA RUE'S INCANDESCENT LAMP. 1820
In this lamp, the first one on record, a platinum wire operated in vacuum.

Davy's Discovery of Electric Light

Sir Humphry Davy was a well known English chemist.
About 1802, with the aid of a powerful battery that he had
constructed, he made a number of experiments on the
chemical effects of electricity. He decomposed a number
of substances and discovered several elements, among
which were boron, potassium and sodium. He gave several
lectures before the Royal Society and incidentally demon-
strated that electricity would heat thin strips of metal to
a white heat, causing them to oxidize so rapidly in the air
that they hterally burned up. Platinum, he found, would
not oxidize as readily, so that it could be heated to a white
heat and give light for a considerable length of time. This

25

THE INCANDESCENT LAMP

was the forerunner of the incandescent lamp, but it was not
until 1879 that a lamp suitable for general distribution was
invented.

About 1809, Davy also demonstrated the arc light. This
he did with a battery of two thousand cells, the terminals
of which were connected to two charcoal sticks. A brilliant
arch shaped flame was produced when the two charcoal

(DROVES' IXCAXDESCEXT LAMP. 1840
A coiled platinum wire burner was covered by a glass tumbler
surrounded by water in glass dish to protect the burner from
draughts of air.

sticks were allowed to touch each other and then pulled
apart, the name "arc" being given to this light on account
of the shape of the flame.

The First Attempts at Making an Incandescent Lamp

The earliest record of any attempt at making an
incandescent lamp was in 1820, when De la Rue made a lamp
with a coil of platinum wire for a burner which was enclosed
in a piece of glass tubing, the ends of which had brass caps.
It was supposed to have had a vacuum, but how this was
accomplished is not clear.

26

THE INCANDESCENT LAIMP

Platinum has to operate very close to its melting tem-
perature before it becomes incandescent. At this operating
temperature it disintegrates rapidly, so that such a lamp
would not last long. The cost of current from the batteries
then available made its operating cost prohibitive, so the
lamp is of historic interest onh^

DE MOLEYN'S INCANDESCENT LAMP. 1841
This lamp is of interest as being the first one on which a patent
(British) was granted. The lamp contained powdered charcoal
which filled and bridged the gap between two coils of platinum wire
mounted in a globe from which the air had been exhausted.

In 1840, Grove gave a lecture before the Royal Society
and demonstrated his battery by lighting the auditorium
with incandescent electric light. His lamps consisted of a
coil of platinum wire fastened to the ends of copper wires,
the lower part of which were varnished for insulation. The
platinum wire burner was covered by a glass tumbler to
protect it from draughts of air, which would otherwise cool
it. The open end of the tumbler was set in a glass dish

27

THE INCANDESCENT LAMP

partly filled with water through which the varnished cop-
per wires extended, and which thereby made a seal pre-
venting any draught of air from reaching the burner.

The platinum had to be operated very close to its melting
point before it became sufficiently incandescent to give any

STARR'S PLATINUM LAMP, 1845
This lamp had a strip of platinum for a burner whose active length
was adjustable to fit the size of battery used. It operated in air
but was covered by a globe to protect the burner from draughts.

light. A great deal of current was also required to keep the
platinum incandescent as the air in the tumbler tended to
cool it by conducting the heat away. It is estimated that
the cost of current with Grove's battery was at the rate of
several hundred dollars a kilowatt-hour. As a comparison,
the present general average retail rate at which current is

28

THE INCANDESCENT LAMP

STARR'S CARBON LAMP. 1845

This consisted of a rod of carbon operating in the vacuum above a

column of mercury.

sold by central station lighting companies is now about
eight cents a kilowatt-hour.

The first patent on an incandescent lamp was granted
by the British Government in 1841 to Frederick De
Moleyns. His lamp was quite novel, consisting of a spheri-
cal glass globe in the upper part of which was a glass tube

29

THE INCANDESCENT LAMP

containing powdered charcoal. This tube was open at the
bottom and through it ran a platinum wire coiled at the
end inside the globe. Another platinum wire extended
upward from the bottom of the globe, terminating in a
coil whose end was close to that of the first coil. The
powdered charcoal in the glass tube filled the two coils

STAITE'S LAMP. 1848

The burner was of platinum and iridium operating in air but covered

by a globe.

of platinum wire, bridging the gap between them. Current
flowing from one platinum wire to the other through the
bridge of powdered charcoal made the latter incandescent.

Starr's Contribution to Incandescent Lamp Development

J. W. Starr was an American from Cincinnati, Ohio,
who induced George Peabody, the philanthropist, to back
him in his research work. He went to England and in 1845
obtained a patent on two incandescent lamps he had in-
vented. This patent was taken out under the name of
King, his attorney.

30

THE INCANDESCENT LAMP

One lamp consisted of a strip of platinum, the active
length of which could be adjusted to fit the strength of the
battery used so that the burner would operate at the
proper temperature. It was covered by a glass globe to
protect it from draughts of air.

Starr's other lamp consisted of a carbon rod operating in
the vacuum above a column of mercury (Torrecellium vac-
uum) as in a barometer. A platinum wire was sealed in
the upper end of a tubular glass bulb, inside of which was a
thin slab of carbon attached to the platinum wire by an
iron clamp. The lower end of the carbon slab was attached
by another iron clamp to a long copper wire. Fused to the
bottom end of the tubular glass bulb was a narrow glass
tube, open at the end, and a little over thirty inches in
length, into which the copper wire extended. The bulb with
its extended glass tube was filled with mercury and set in
a dish containing mercury after the fashion of a mercury
barometer, so that the mercury ran out of the bulb and
came to rest in the tube at about 30 inches above the
surface of mercury in the dish.

This lamp, however, was impractical, as it is now known
that such a vacuum contains water vapor, and that when
the lamp is Hghted, the heat will drive gases out of the glass,
the carbon rod, iron clamps, etc., which will cause it to
blacken rapidly.

Unfortunately, Starr died on board ship, while re-
turning to the United States in the following year (1846).
He was only 25 years old.

Other Experimental Incandescent Lamps

During the next few years, several inventors tried to
make incandescent lamps, even though it was known that
their use with current obtained from batteries would be
impractical. The dynamo was being improved but was
still impractical commercially.

In 1848, W. E. Staite made a lamp having a burner
consisting of platinum and iridium operating in the air, but
covered by a glass globe to protect it from draughts. It

31

THE INCANDESCENT LAMP

had a thumb screw for a switch, the whole device being
mounted on a bracket, the arm of which was to be the
return wire.

Edward C. Shepard, in 1850, made a lamp consisting of a
weighted charcoal cylinder pressing against a charcoal cone
in vacuum. The high resistance contact became incandes-
cent when current flowed through it.

SHEPARD'S LAMP. 1850

The high resistance contact between a weighted charcoal cylinder

pressing against a charcoal cone in vacuum made the charcoal

incandescent.

M. J. Roberts, in 1852, made a lamp having a graphite
rod operating in vacuum. The open end of the glass globe
surrounding the burner was cemented to a metal cap, to
which was screwed a pipe containing a stop cock. Through
this pipe the air could be exhausted, the stop cock closed,
and the lamp then mounted on a stand. The graphite rod
was held by a clamp at the end of two metal rods, one rod
being fastened to the pipe and the other being insulated
from but passing through the metal cap. The lamp was
not successful because such an arrangement could not
maintain a good vacuum for any length of time.

32

THE INCANDESCENT LAMP

In 1856, De Changy, a French civil engineer, obtained a
Belgian patent on a lamp having a coiled platinum wire for
the burner which operated in air but was covered by a
glass tube to protect it from draughts. It was a portable

ROBERTS' LAMP, 1852 DE CHANGY'S LAMP. 1856

This consisted of a graphite rod This had a platinum burner oper-

operating in vacuum. ating in air but covered by a glass

tube. It was designed for use in
a mine, being so arranged that it
could be hooked to wires fastened
on the walls throughout the mine
and thus be located in the places
desired.

affair having hooks for terminals, and was intended specially
for use in mines. A pair of wires could be fastened to the
walls and run throughout the mine; the lamp could be
located in different places as desired by simply hooking
it to the wires.

33

THE INCANDESCENT LAMP

Professor Moses G. Farmer, of the Naval Training
Station at Newport, Rhode Island, made a lamp in 1859,
several of which were used to light the parlor of his home,
11 Pearl Street, Salem, Mass., during July of that year. The
lamp consisted simply of a strip of sheet platinum operating
in air, the novel feature being that the strip was narrower
at the ends than in the middle. This caused it to be
more uniformlv incandescent throughout its entire length,

FARMER'S LAMP. 1859
Prof. Farmer, during July, 18.59, lighted the parlor of his home at
Salem, Mass., with several of these lamps. The platinum burner
was narrowed at its ends so that the entire length became more uni-
formly incandescent.

the higher resistance of the narrowed ends consuming pro-
portionally more electrical energy, and thus offsetting the
loss of heat which was conducted away by the terminals of
the lamp. He obtained a U.S. patent on this feature many
years later, (1882).

Swans Contributions

Sir Joseph W. Swan, who became one of the foremost
incandescent lamp manufacturers in England, made at
various times, from 1848 to 1860, a number of experimental

34

THE INCANDESCENT LAMP

lamps. These consisted of carbonized strips and spirals of
paper and cardboard, coated with various liquids, which on
being heated left a large residue of carbon. These lamps
were operated in vacuum, either in a glass bottle having a
wide neck closed with a rubber stopper through which the
connecting wires passed, or in a glass bell whose rim made
a tight fit within the rim of a brass plate through which
one insulated connecting wire passed, the plate being used

■jimu m\siSisisi!L

SWAN'S LAMP, 1860.

A strip of carbonized paper was covered by a glass bell fitting tight on

a brass plate and operated in vacuum.

as the other connection. Owing partly to some trace of air
being left within the glass container, and partly to the
carbons becoming distorted, the lamps soon broke down.

The pumps used to produce a vacuum consisted of a
plunger operating in a cylinder with valves. This produced
a relatively very poor vacuum compared with that now
possible. In 1865, Herman Sprengel, by his invention of
the mercury vacuum pump, had been able to get a vacuum
far superior to any previously attainable. This pump con-
sisted of a long glass tube held vertically, the bottom end
being dipped into mercury in a container. The upper end
had two branches, one connected to a supply of mercury

35

THE INCANDESCENT LAMP

and the other to the device from which the air was to be
exhausted. The mercury, in flowing down the tube, trapped
bubbles of air, the weight of the mercury forcing these air
bubbles down the tube and out into the outside atmosphere.
Thus in time the flow of mercury would exhaust the air
from the device.

In 1875, Crookes (afterwards Sir WilHam Crookes),
astonished the world by the exhibition of his radiometer
and the description of the improved means he employed, in
connection with the Sprengel pump, for obtaining the near
approach to a perfect vacuum which the construction of the
radiometer demanded. The publication of this paper led Sir
Joseph Swan to resume his incandescent lamp experiments.

In 1877, Swan, through a chance advertisement about
radiometers, got a young bank clerk, Charles H. Stearn, to
assist him in carrying out these experiments. Stearn had
been pursuing investigations which required high vacuum
and was familiar with the manipulative requirements
necessary for obtaining a very high degree of evacuation.

A series of experiments were started by Stearn with
carbon conductors of various forms and sizes, which
Swan supplied, beginning with the strips and spirals of
carbonized paper and cardboard formerly used, and which
Swan had firmly fixed in his mind, would be durable when
operated to incandescence in a very perfect vacuum. These
were mounted in glass bulbs which were exhausted to the
highest possible degree by means of the Sprengel pump.

Great difficulty was at first experienced in making firm
contact between the ends of the carbon strip and the
conducting wires to which it was held. To avoid the manip-
ulative difficulties and to arrive more rapidly at a definite
settlement of the question whether and under what condi-
tions a carbon conductor would be durable, the thin
strips and spirals were, for the time being, discarded and
other forms of carbon conductors were tried. Among the
forms used were carbon wires, both straight and bent in an
arch, made of the same plastic material commonly used in
carbon rods for arc lamps.

36

THE INCANDESCENT LAMP

Notwithstanding the fact that the lamp bulb had been
highly evacuated, the vacuum rapidly deteriorated owing
to the evolution of gases from the carbon which took place
as soon as current was turned on. This difficulty was over-
come by heating the bulb by a flame from the outside and
then passing a strong current through the carbon to make

SWAN'S LAMP. 1878
A carbon wire operated in a high vacuum in an all-glass globe.

it brilHantly incandescent while it was still connected to
the exhaust pump. The straight carbon wires were found
to buckle and so did not last, but the arch shaped carbon
wires gave good results.

When the incandescent lamp became commercially
available, Swan invented, early in 1880, the parchmentized
thread which, when carbonized, produced a long thin

37

THE INCANDESCENT LAMP

carbon that was used by some manufacturers for many
years. He discovered that cotton thread treated with
sulphuric acid became agglutinated and lost its fibrous
condition, having the appearance and the hardness of cat-
gut when dried. This material could even be planed and
scraped down to a fine wire of the most perfect roundness
and could be bent into spirals which retained their shape
during carbonization. The difficulty previously experienced

LODYGUINE'S LAMP, 1872
This had a graphite burner operating in nitrogen gas. An experimen-
tal installation of two hundred of these lamps was made to light the
Admiralty Dockyard at St. Petersburg.

in making firm contact between the ends of the fine
carbon and the conducting wires was overcome by making
enlarged ends on the carbons which were held in tiny silver
or copper sockets, similar to that of a crayon holder, and
secured with a slip ring. Later on improved means were
devised for making good electrical contact by means of a
contrivance developed by Swan and Gimingham w^hich con-
sisted in tubulating the ends of the conducting wires,
inserting the ends of the carbons in the tubes and causing
a deposit of carbon to take place at the junction.

38

THE INCANDESCENT LAMP

Russian Incandescent Lamp Inventors

In 1872, Lod\^guine, a Russian scientist, made a lamp
having a "V" shaped piece of graphite for a burner which
operated in nitrogen gas. This was covered by a glass globe
fastened to a metallic cap with a gasket to make a tight

KOSLCFF'S LAMP, 1875
This had several graphite rods, one
operating at a time. When one
burned out, another was automat-
ically connected. The rods operated
in nitrogen gas.

KOXX'S LAMP, 187.5
This lamp was similar to that of
Kosloft's except that the graphite rods

operated in vacuum.

joint. He installed two hundred of these lamps about the
Admiralty Dockyard at St. Petersburg. In 1S74 the Russian
Academy of Sciences awarded him the Lomonossow Prize of
fifty thousand rubles, then worth about $25,000, for his
invention. A company was formed with a capitalization of

39

THE INCANDESCENT LAMP

BOULIGUINE'S LAMP. 1876
This had a long graphite rod operating in vacuum. Only the upper
part of the rod was in circuit and as this part burned out, the rod was
automatically shoved up, thus placing a fresh portion in circuit.

200,000 rubles to exploit the lamp, but the project soon
failed as the lamp was too expensive to operate.

In 1875, Kosloff, another Russian, made a lamp con-
sisting of several graphite rods operating in nitrogen.
The rods were so arranged that only one operated at a time

40

THE INCANDESCENT LAMP

and, when it burned out, another was automatically con-
nected in circuit. Konn, also a Russian, invented a lamp
in 1875, similar to that of Kosloff, except that the graphite
rods operated in vacuum. The next year, 1876, Bouliguine,
another Russian, made a lamp having a long graphite rod,
only the upper part of which was in circuit. When this
part burned out, a counterweight automatically pushed
the rod upward thereby placing a fresh portion of the
long rod in circuit. It operated in vacuum.

Commercial Introduction of the Arc Lamp

None of these incandescent lamps was practical ; they had
short lives, were expensive to operate, were unreliable in
their operation, and so were not commercially used. By
this time, however, the arc lamp was being introduced
commercially, the pioneer installation being that of
Jablochkoff, who Ht the boulevards in Paris with his
"electric candle." This simple arc lamp consisted of two
carbon rods held together side by side and insulated from
each other by kaolin. The kaolin vaporized as the carbons
were consumed, giving the arc a peculiar color. A complete
system was developed by Jablochkoff, consisting of an
alternating-current generator, having a stationary exterior
armature with internally revolving field poles. Alternating
current was used to offset the difficulty experienced with
the unequal consumption of the carbons on direct current.
A series system of distribution was used and, in order to
prevent interruption of the circuit should one "candle"
go out, several candles were put in each fixture with an
automatic device to connect a fresh candle whenever
one burned out.

In the United States there were several pioneer arc light
systems. The earhest were those of William Wallace, of
Ansonia, Connecticut, who became associated with Prof.
Moses G. Farmer; Edward Weston, of Newark, New Jersey,
the well known maker of electrical measuring instruments;
Charles F. Brush, of Cleveland, Ohio; and Prof. EHhu
Thomson, w^ho became associated with Edwin J. Houston,

41

THE INCANDESCENT LAMP

and formed the Thomson-Houston Company, a fore runner
of the General Electric Company.

Thus, in 1877, the arc lamp was commercially established,
dynamo electric machines were available, and a demand
had arisen for a smaller electric light than the arc lamp.

SAWYER'S LAMP, 1878
This was one of several developed, all
having a graphite burner operating in
nitrogen gas. The heavy fluted copper
wires were used to radiate the heat
and thus maintain a cool joint between
the glass cover and metal holder.

FARMER'S LAMP, 1878
This also had a graphite rod operating
in nitrogen gas. This lamp is on exhibit
at the United States National Museum
at Washington, D.C., through whose
courtesy this photograph is shown.

*' Subdividing the Electric Light"

In this country there were four men who were energeti-
cally attacking the problem, popularly called "sub-
dividing the electric light," the arc lamp being the only then
known electric light. This phrase was really a misnomer, be-
cause the arc lamp was not subdivided into small units, a
practical incandescent lamp being the final result of the ex-
periments. These four men were: William E. Sawyer, Prof.
Moses G. Farmer, Hiram S. Maxim, and Thomas A. Edison.

42

THE INCANDESCENT LAMP

Sawyer became associated with Albon Man, his patent
attorney, who gave him financial assistance. The Sawyer-
Man Electric Company was organized and several lamps
were developed. They all consisted of a piece of graphite
operating in nitrogen, covered by a glass globe cemented to

MAXIM'S GRAPHITE LAMP, 1
A graphite rod operated in a rarefied hydro-carbon vapor. An electro-
magnet short circuited the burner when the current became too
strong. This lamp is also on exhibit at the United States National
Museum, through whose courtesy this photograph is shown.

a metal holder. Heavy fluted copper wires were used to
make connections with the burner through the holder, in
order to radiate the heat and thereby maintain a cool joint
between the glass globe and holder. The lamps were
designed so that they could be renewed by opening the

43

THE INCANDESCENT LAMP

joint and putting in a fresh burner. The company failed,
but was later reorganized after Edison's invention of a
practical lamp. This company was a forerunner of the
present Westinghouse Lamp Company.

Farmer made a lamp consisting of a graphite rod which
also operated in nitrogen gas. It was covered by a glass bulb
having a rubber stopper through which copper rods con-
necting with the burner were passed. A tube was put in the
rubber stopper through which the air was exhausted and
nitrogen gas put in.

Maxim, well known for his later invention of the rapid
fire gun, made two lamps. One consisted of a piece of sheet
platinum operating in air. The main feature of this lamp was
that when the platinum, held at the top by an adjustable
bolt and nut, became too hot and dangerously near its
melting temperature it would expand sufficiently to make
contact with a wire which short circuited the burner. This
shunted the current from the platinum burner, allowing it
to cool for a fraction of a second so that it shrunk, opening
the short circuit and allowing current to flow again through
the burner. The other lamp consisted of a graphite rod
operating in a rarefied hydrocarbon vapor and protected
from excessive current by an electro-magnet which short
circuited the graphite burner.

44

CHAPTER TWO

Edison's Invention of a Practical Incandescent

Lamp, and a Complete Lighting System, and

Their Commercial Introduction

Edison first began his study of the incandescent lamp
problem in the fall of 1S77. He had a well equipped labora-
tory at Menlo Park, New Jersey, with several able assistants
and many workmen, about a hundred people all told. He
had already made several important inventions, among
which were ; the quadruplex telegraph, whereby four mes-
sages could be sent simultaneously over one telegraph
wire, thereby quadrupling the capacity of the telegraph
lines of the country; the carbon telephone transmitter,
without which Bell's telephone receiver would have been
impracticable; and the phonograph. The lasting value of
these inventions proved that Edison was eminently fitted
to attack the problem of "subdividing the electric light."

Edison first made many experiments with the object of
confirming the failures of others. In July, 1878, his health
having been undermined by his unceasing work, he took a
trip w4th an expedition to Wyoming to observe an eclipse
of the sun. This he called a "vacation", but he brought
with him a delicate instrument he had invented which he
called a tasimeter. This was devised to measure the heat
transmitted through great distances. In about two months
he returned to Menlo Park and again studied the lamp
problem, which was but one among many others he was
trying to solve.

His first experiments having shown the seeming im-
practicability of carbon for the incandescent burner, he
started investigating platinum. He developed a lamp hav-

45

THE INCANDESCENT LAMP

EDISON'S MENLO PARK BUILDINGS
On the left is the wooden laboratory building, in the left background
is the brick machine shop. The brick building in the rictht foreground
IS the office and library.

EDISON AND SOME OF HIS CO-WORKERS

The men are assembled on the front of the laboratory building. They
are, from left to right — • top row: J. W. Lawson, unknown, unknown,
L. K. Boehm, Charles Batchelor, Francis Jehl, F. R. Upton, and
Dr. A. Haid; second row: J. F. Kelly, David Cunningham, T, A.
Edison, Major F. McLaughlin and T. Logan; third row: J. F.
Randolph, Charles Flammer, George Dean, George E. Carman,
John F. Ott, James Seymour and unknown; bottom row: A. Swanson,
Martin N. Force, S. L. Griffin, and Milo Andrus.

46

THE INCANDESCENT LAMP

MODEL OF EDISON'S LABORATORY BUILDING
This model was made by F. A. Wardlaw, one of Edison's early asso-
ciates. Each part of the model is made from the original parts of
the building itself down to the last detail; the shingles, clapboards,
piazza railing and posts, flooring, bricks in the chimney, etc., and
even the glass in the windows. Photograph courtesy of the Asso-
ciation of Edison Pioneers.

INTERIOR OF EDISON'S LABORATORY BUILDING, 1880
This photograph was taken February 22, 1880. Several lamps will be
seen mounted on the converted gas ftxtures hanging from the ceiling.
Edison is seated in about the center, his principal assistants gath-
ered about him.

47

THE INCANDESCENT LAMP

ing a platinum spiral for a burner. Inside the spiral was a
rod which expanded when the platinum became heated,
and if the temperature became too high, the expansion of
the rod would cause it to short circuit the burner, thereby
allowing the platinum to cool. This took but a fraction of
a second, and the rod, contracting almost immediately,
opened the short circuit. Thus the lamp only "blinked"

EDISON'S FIRST PLATINUM LAMP, 1878
This was the first of a number of lamps he built in his study of making
a practical incandescent lamp. It is in the William J. Hammer
Collection of Historical Incandescent lamps. Photograph, cour-
tesy of Major Hammer and the Association of Edison Illuminating
Companies, in whose custody this collection is kept.

when the current was too high. A patent was applied for
in October, 1878, and Edison's first lamp patent was
granted in April, 1879.

Up to this time Edison had spent quite a lot of money
in lamp research, and, in order to raise more money to
continue the work, a corporation was organized. On
October 17, 1878, the Edison Electric Light Company,
with a capital of $300,000, was incorporated by several
prominent men for the purpose of backing Edison in his

48

THE INCANDESCENT LAMP

work of trying to develop a complete incandescent electric
light system. This company was a forerunner of the present
General Electric Company.

Edison's next step in lamp research was to make a more
sensitive thermostatic arrangement to short circuit the
platinum burner. This was accompHshed by means of an
expanding diaphragm, a patent being applied for in
November, 1878, and granted early the next year. He then
made a lamp using platinum foil for the burner. A patent
was appHed for on this lamp in December, 1878, and granted
in August of the following year.

His next development was a lamp having an inverted
"U" shaped burner consisting of finely divided iridium
mixed with oxide of zirconium. The latter is a non-
conductor of electricity when cold, but iridium made the
composite burner a conductor and, when heated, the
zirconium oxide also became a conductor. A patent on
this was appHed for in December, 1878, and granted in
September, 1879.

Edison's next appHcation for a lamp patent was made
in February, 1879, and covered a long carbon rod pressed
upward by a heavy counterweight against a platinum-
iridium rod. The light was obtained from the current
heating the resistance of the poor contact between the
rods. As the heat consumed the end of the carbon rod,
it was automatically fed upward by the counterweight.
The platinum-iridium rod was also slowly consumed. A
patent for this lamp was granted in February, 1880.

Edison's Study of a Complete Incandescent Lighting System
None of the lamps he had made was practical and fur-
thermore he reaHzed that even if he was finally able to make
a lamp that would be commercial, it would be impractical if
operated on the series system of distributing electricity, as it
would be impossible to turn on or shut off one lamp with-
out doing the same thing to all the others on the circuit. In
this system the current is constant throughout the circuit,

49

THE INCANDESCENT LAMP

the current flows out of the armature of the dynamo through
one brush, through the field coils, through one lamp after
another and then back to the armature through the other
armature brush. This system was satisfactory for arc lamps,
which are inherently a constant current device, and was also
suitable for use in street lighting for which arc lamps were
most generally used, as in that case there was no need to
turn on one lamp at a time.

=^'

g:

H

^Cons+anf Currerri- Dvjnamo

o — o — o — a

o — o — o — o—

DIAGRAM OF CONSTANT CURRENT SYSTEM
Prior to 1878, this was the only known method of distributing
electric current.

w

^Con slant Vol+age Dynamo

DQii ^ ^ ^ ^ <^ <>

DIAGRAM OF EDISON'S MULTIPLE SYSTEM
In 1878, Edison invented this system of distributing electricity at a
constant pressure and in quantities as required. It is now
universally used.

Edison therefore reasoned that another system of dis-
tributing electricity to lamps must be used, patterned
after the existing gas light system, as small electric lamps
would find their greatest usefulness in household, com-
mercial, and industrial Hghting. He made an intensive
study of gas, obtaining all the literature possible on the
subject, and spending several weeks of his time in con-
tinuous reading.

50

THE INCANDESCENT LAMP

Gas is distributed through pipes, with mains, feeders
and branches supplying it at about constant pressure
at the lamps. While the gas escapes into the air after
it is burned, electric current must be returned to the
dynamo armature after it goes through the lamps.

After much thinking he evolved a constant pressure
electrical system, which is called the "multiple" system
of distribution. In this system current is generated at a
constant pressure and suppHed in quantities as desired.

EDISON'S CONSTANT VOLTAGE DYNAMO.

This machine was invented by Edison to fit the multiple system he had
also invented. It had an efficiency of 90 per cent which
scientists had mathematically "proved" was impossible.

This required the design of a dynamo to supply such a
current. This was something that had not been previously
done, but undaunted, he attacked the problem.

After much intensive study, he designed a dynamo
having an extremely low resistance in the armature.
He made a drum wound armature, using large heavy wires
in place of small ones in order to reduce the resistance. The

51

THE INCANDESCENT LAMP

field coils were connected directly across the armature in
multiple, instead of in series with it. When the machine
was run at a certain constant speed, the voltage (pressure)
between the two armature brushes was approximately 110
volts and remained about constant, falling but slightly with
increasing amounts of current taken from the machine. Up
to a certain point, the capacity of the machine, this could
be done without undue heating of the armature. He found
by tests that the machine, at about full load, converted
90 per cent of the mechanical energy required to drive it
into electrical energy, or in other words, it was 90 per cent
efficient.

When he announced the invention of this dynamo,
some scientists ridiculed it, as it had been proven that the
greatest amount of electrical power which could be obtained
from a battery was at that point where the internal resistance
of the battery was the same as the resistance of its external
load. Under these circumstances the battery would have
an efficiency of 50 per cent and scientists thought that this
should be the condition at which a dynamo could be
operated to the best advantage.

Development of a High Resistance Platinum Lamp

Edison now had a dynamo that would give a constant
voltage of about 110 volts between the two wire conductors
leading from the armature, to which one or more lamps
could be connected. By applying Ohm's law, he reasoned
that the smaller the amount of electrical power a lamp
for this system should take, the higher should be its resist-
ance. For example, suppose an incandescent lamp is
to be made to consume 550 watts, which was about the
rating of the arc lamps then made, but that this lamp
should be designed for use on 1,10 volts. As the watts
are equal to the volts times the amperes, a 550-watt, 110-
volt lamp will consume 5 amperes, and by Ohm's law,
which is that the amperes equal the volts divided by the
ohms, this 550-watt lamp will have a resistance of 22
ohms. Similarly a 110-watt, 110- volt lamp would have a
resistance of 110 ohms.

52

THE INCANDESCENT LAMP

The current in the series circuits on which arc lamps
were then commercially operated was about ten amperes,
although some systems were later designed for twenty
amperes. The lamps that Edison had made previously were
designed for use on these 10-ampere circuits and consumed
about 110 watts. The voltage across the terminals of the lamp
was therefore 11 volts and the resistance of the lamp burner
1.1 ohms. Thus the resistance of the lamps he had previ-

EDISON'S FIRST HIGH RESISTANCE LAMP, 1879
This had a long, thin platinum wire mounted on pipe clay and coated
with zirconium oxide. It had a diaphragm thermostat which cut
off the current momentarily if the burner got too hot. This lamp
is in the Hammer Historical Collection of Incandescent Lamps.
Photograph, courtesy of Major Hammer and the Association of
Edison Illuminating Companies.

ously made had to be increased from 1.1 to 110 ohms before
they would be suitable for his 1 10-volt multiple system.

All this reasoning may be difficult for the layman to
understand. It was for most electricians in 1879, as they
did not thoroughly understand Ohm's law. It was there-
fore no small accomplishment, although it may not seem so

53

THE INCANDESCENT LAMP

now to those familiar with electrical engineering, for Edison
to have developed such a new and complete system of
distributing electricity.

The first high resistance lamp that Edison designed had
a long thin coiled platinum wire mounted on a piece of
pipe clay and coated with oxide of zirconium to protect
the platinum from oxidizing. In order to prevent the
burner from operating at too high a temperature, it was
protected by his diaphragm thermostat, but in this case
the circuit was opened to cut off the current from the
platinum wire. This was necessary because if the scheme
used in former lamps for series circuits of short circuiting
the burner were used in the lamp for the new multiple
system, the low resistance of the short circuit across the
constant pressure would cause such a heavy rush of current
to flow that it would melt the conductors almost instan-
taneously. A patent for this lamp was applied for in Febru-
ary, 1879, and was granted in May, 1880.

Oxide of zirconium, while an insulator when cold, will
decrease materially in resistance as it gets hotter. Cur-
rent, instead of flowing through the long thin platinum wire,
would then be shunted through the zirconium oxide coating
between the turns of the coiled platinum wire, heating
the latter to such high temperature that the lamp would
short circuit itself. The lamp was therefore impractical.

During his experiments, Edison had found that platinum
became extremely hard after it had been heated several
times by the current flowing through it. This made it
possible to operate it at much higher temperatures without
danger of melting and so give much more light. He believed
that the heat drove gases out of the minute pores of the
platinum, causing it to become more dense by sintering the
particles of platinum closer together. He then thought
that if the platinum were operated in vacuum, more gases
would escape from it so that it could perhaps be operated
at even higher temperatures.

He therefore wound a long thin platinum wire on a spool
of pipe clay, but this time he omitted the zirconium oxide

54

THE INCANDESCENT LAMP

coating. The platinum coil was mounted in a one-piece
all-glass globe, all joints being fused by melting the glass
together. The ends of the platinum wire passed through
the glass, which was fused around the wire to make an air
tight joint. The all-glass globe was considered necessary
to maintain the high degree of vacuum then obtainable
with the recently invented Geissler and Sprengel mercury
vacuum pumps. The glass globe was then put inside a glass
cover mounted on a holder within which was mounted a
diaphragm thermostat which protected the platinum wire
from excessive temperature. A patent for this lamp was
applied for in April, 1S79, which was granted in May, ISSO.

This lamp was apparently successful, so a number of
them were made to try out. But, since they consumed a lot of
power in proportion to the light they gave, were short lived,
and very expensive to make, they were not considered com-
mercially practical. The platinum lamp had, it seemed,
reached the limit of its possibilities so the problem appeared
impossible of solution and, for a time, was abandoned.
Solittion of the Incandescent Lamp Problem

Edison had done a lot of experimenting with different
forms of carbon for his telephone receiver, which gave him
a broad knowledge of the properties of carbon. Several
months had passed since he had worked on the incandescent
lamp and in the fall of 1879, he began thinking about it
again. He knew that carbon had a high resistance com-
pared with platinum. In order to get the requisite resist-
ance, he realized that the carbon would have to be very
slender. Thick carbon rods did not last very long when he
subjected them to the high temperature of incandescence,
so a slender piece should seemingly last but a very short
time. He wondered, however, if it would last any longer in
the high vacuum he had been able to obtain with his plat-
inum lamp. It seemed foolish to try this but in order to
leave no stone unturned he made the bold attempt.

The first problem was that of obtaining carbon of the
requisite slenderness, and of determining what its length
and diameter should be. After considerable calculation he

55

THE INCANDESCENT LAMP

estimated that the carbon should be not over a sixty-fourth
of an inch in diameter, or about the size of ordinary heavy
sewing thread. From that he conceived the idea of the
possibiHty of carbonizing a piece of sewing thread by heating
it in an air-tight crucible. This in itself was a bold thing to
do, for it would not require the presence of much air in
order to have the thread burn up. He estimated that the
carbon should be about six inches long.

Carbonizing a substance consists of heating it away from
the presence of air so that the heat does not oxidize the
material, but merely drives off the volatile matter, leaving
only the carbon residue behind. This is similar to distil-
Hng coal, which is put in closed retorts, heat being applied
from the outside. The heat drives out a number of volatile
gases from which the coal gas is obtained, which, when
enriched with oils, becomes illuminating gas. Coal and
many other substances contain hydro-carbon compounds
and the heat decomposes them, leaving a carbon residue
behind which is known as coke.

Edison cut several pieces of sewing thread and packed
them in with a lot of powdered carbon in an earthenware
crucible. The threads were packed so that they were "U"
shaped in order to reduce the size of the glass globe in
which they were to operate. The powdered carbon was
partly for the purpose of minimizing the amount of air in
the crucible and partly to absorb the ox^^gen in what little
air there was left. The crucible was then covered with an
earthenware top, the two being cemented together Ai^ith fire
clay to further exclude any air.

The crucible was then put in a furnace and subjected
to a high temperature for several hours. It was then allowed
to cool gradually, which took many hours before the inside
had become cool enough to prevent the threads from
burning up in unpacking. After many patient trials he
finally obtained an unbroken carlDonized thread, "filament "
he called it, which then had to be fastened to a pair of
platinum wires. This was finally done, after many failures,
by delicate clamps. The platinum wires had been sealed

56

THE INCANDESCENT LAMP

in a piece of glass tubing and the filament was then fastened
to the ends of the platinum by the clamps. This mounted
filament was then inserted in a glass bulb, the glass
tubing being fused to the neck of the bulb to make an
air-tight joint. On the opposite end a small glass tube
had been fused for the purpose of exhausting the air from
the bulb.

EDISON'S SUCCESSFUL HIGH RESISTANCE CARBON
LAMP

On October 21, 1879, Edison made this experimental lamp which
embodies the basic features of all lamps made today. It consisted
of a carbonized cotton thread operating in a very high vacuum
maintained by a one piece all glass globe. This replica was made
by Francis Jehl, one of Edison's pioneer assistants, by whose
courtesy this photograph is reproduced. The origmal experimental
lamp was destroyed.

The lamp was then connected to the mercury vacuum
pump until the vacuum reached a high degree. Edison,
however, believed from his experience with platinum that

57

THE INCANDESCENT LAMP

gases would also be "occluded" in the carbon filament, so
in order to drive them out, he put a small amount of current
through the filament to heat it slightly. Immediately the
gases began to come out and it took nearly eight hours on
the pump before they apparently ceased.

The crucial time had come to try the lamp out. The
men in the laboratory were skeptical about it and bets
were made that it would last but a few minutes. With a
crowd about him, Edison turned the current on gradually
by means of external resistance until the filament glowed
dimly. It did not burn out. Becoming bold he gradually
cut out the resistance until the lamp gave a brilliant light.
Still it did not burn out. It continued to burn, and when
evening came it was still going strong. This was October
21, 1879, and the lamp burned steadily for nearly two
days.

Edison now felt that he was on the right track, and every
thing conceivable was carbonized in the endeavor to make
a better filament. After many weeks of working almost
continuously day and night, he found that carbonized
paper (bristol board) would give several hundred hours life.
He then felt that he had a practical lamp which could be
commercially used, so he decided to announce his invention
and demonstrate it to the public.

The announcement was made in an article which took
the entire first page of the New York Herald of Sunday,
December 21, 1879. Several scientists proclaimed Edison's
invention to be a fake. Gas stocks, however, dropped in
price and stock in the Edison Electric Light Company
soared to thirty-five hundred dollars a share.

The demonstration consisted of about sixty lamps
mounted on poles lighting the laboratory grounds and coun-
try roads in the neighborhood. Wires were also run to
several houses and lamps installed in them. Crowds came
out to Menlo Park during the next few days and the
Pennsylvania Railroad had to run special trains to accom-
modate them.

58

THE INCANDESCENT LAMP

r i.F^uatc: n !-7« -vTAPRTPLK .CBECT-WITH STPPLEMSMT.

SKW YORK BKILM

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mnVI IBMTliS OF

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ANNOUNCEMENT OF EDISON'S SUCCESS

This article appeared in the New York Herald oi December 21, 1879, just
two months after the "birth" of the lamp. Scientists proclaimed
it a fake. Nevertheless the price of gas stocks dropped and stock in
the Edison Electric Light Company soared to $3500 a share.

THE INCANDESCENT LAMP

-.

Edison applied for a patent on this lamp on November
4, 1879, and on January 27, 1880, the basic lamp patent
No. 223,898 was granted him. All the elements of this lamp
are the same as those in the lamps made today; a high resist-
ance filament operating in a high vacuum, maintained by
a one piece all-glass globe having all joints sealed by fusion
of the glass. While some lamps made today are filled with
an inert gas after the lamp has been exhausted, the features
are otherwise the same.

M3J

^^^^'^'^Wfi^^m^,M:M

DEMONSTRATION OF EDISON'S INCANDESCENT
LIGHTING SYSTEM, 1879.
Lamps were mounted on poles lighting the neighborhood of ^e
Laboratory at Menlo Park. The various buildings of the
Laboratory can be seen in the background.

Edison's Invention

There has been some misconception of exactly what
Edison did invent. He was not the first man to make an
incandescent lamp, as has been indicated in the previous
chapter. The principle of incandescent Hghting had been
established and demonstrated by several experimenters
but no lamp previously made was suitable for use in large
numbers over a large area like a city. His analysis of the
problem brought him to the conclusion that such lamps

60

THE INCANDESCENT LAMP

must be connected to the circuit in multiple so each one
would be independent of the others. He also realized that
lamps connected in multiple must be of high resistance, for
the higher their resistance the smaller were the conductors
necessary to carry electricity to them. So he aimed to make
a lamp of the highest practical resistance and he named
this high resistance carbon burner a "filament."

He found that a carbon filament to be of high resistance
must be made very thin and quite long and he also found
that such filaments required a very good vacuum to pre-
serve them. He also soon realized that glass chambers
made in two separate parts, as previous lamps had been
made, would not keep the very good vacuum necessary
to preserve the filament. He then made the very bold step of
fusing the two glass parts inseparably together and making
the glass container closed at all points by fusion of the glass.

That is what Edison invented: a lamp with a high re-
sistance filament of carbon in a vacuum contained in a glass
container closed at all points by fusion of the glass and
having platinum wires imbedded in the glass to carry
current through the glass to the filament. And this was
the first incandescent lamp which was suitable for the
system of general multiple distribution which solved the
problem of the "sub-division of the electric light."

Edison's patent, which the courts upheld as covering
the modern incandescent lamp, covered only a particular
kind of incandescent lamp which combined four elements —
(1) a high resistance filament of carbon, in (2) a chamber
made entirely of glass and closed at all points by fusion of
the glass, which contained (3) a high vacuum and through
which (4) platinum wires passed to carry current to the
filament. It was a patent on a combination of old elements
which produced a new thing — a lamp suitable for multiple
distribution over large areas.

Commercial Installation of the Incandescent Lamp

The first commercial installation of the lamp was made
on the steamship Columbia of the Oregon Railway and

61

THE INCANDESCENT LAMP

Navigation Company. This steamer was being built in
Chester, Pa., and was about completed. She took a trip
to New York and the Edison Electric Light Company
received its first contract to equip the ship with electric
light. Four dynamos were installed run from two overhead
countershafts driven by a pair of vertical steam engines.
Each dynamo had a capacity for sixty lamps, or about six
kilowatts (eight horse power), one dynamo being used as
an exciter for the other three. In this connection Edison

^1 ttvl(''

^^ ^^ '^IBJI^Hj^^^^H

H^^^^^HHUHIH^HIII^^^Kc^

^^^""^ml^M

DYNAMOS ON S. S. COLUMBIA. 1880
This was the first commercial installation of the Edison Lamp and was
started May 2, 1880. One of these dynamos is on exhibition at the
United States National Museum, Washington, D. C.

had made another invention, which by the way scientists
said was impossible, of connecting two or more dynamos
together in multiple, each supplying its proportion of current
to a single circuit. The ship was equipped with 115 lamps
and the plant was started on May 2, 1880. She sailed around
the Horn to San Francisco, where she arrived in July. The
Advising Engineer of the Navigation Company reported

62

THE INCANDESCENT LAMP

that the installation was a complete success. The original
installation ran for fifteen years, when the ship was over-
hauled and a more modern plant installed.

The next commercial installation was started about the
first of the year 1881, in the shop of Hinds, Ketchum &
Company, lithographers, 229 Pearl Street, New York. One
dynamo was installed having a capacity for sixty lamps.

The commercial success of the incandescent lamp was
quickly established. During the two years 1881-82, over

DYNAMOS, HINDS, KETCHUM & CO. 1

This was the second installation, the first on land which was started
about the first of the year, 1881. Photograph, courtesy United
States National Museum.

150 other installations were put in, aggregating over
30,000 lamps. These installations included steamships,
machine and car shops, mills, stores, offices, theaters, hotels,
residences, etc.; all of them were entirely successful.
The First Lamp Factory

The first lamps were made in the Menlo Park Labora-
tory, the glass work being done in a shed there. The shed

63

THE INCANDESCENT LAMP

has been preserved on account of its historical interest and
is now at Mazda Brook Farm (near Parsippany, New
Jersey), a recreation and meeting place for the employees
of the incandescent lamp department of the General Elec-
tric Company.

As so many lamps were now being made, it sorely taxed
the capacity of the laboratory. In the latter part of 1880

THE FIRST INXAXDESCENT LAMP FACTORY, 1880

In November, 1880, the manufacture of lamps was started in this build-
ing, located beside the Pennsylvania Railroad tracks at Menlo
Park, about half a mile from the Laboratory. The four men in the
foreground from left to right, are Phillip S. Dyer, Accountant;
William J. Hammer, Electrician; Francis R. Upton, General Mana-
ger; and James Bradley, Master Mechanic.

a separate company was formed, called the Edison Lamp
Company, to manufacture lamps, and a factory building
obtained, located alongside the Pennsylvania Railroad
tracks at Menlo Park about half a mile from the labora-
tory.

64

THE INCANDESCENT LAMP

During the next year, 1881, the demand for lamps had
so increased that again it became imperative to get more
space. A group of factory buildings were purchased at
Harrison, New Jersey, the present headquarters of the
Edison Lamp Works. Moving was begun in February,
1882, and manufacture in Harrison began in April of that
year, the Menlo Park factory then being shut down. None
of the original buildings at Harrison is now standing.

L

t

16 C.P.. 110 Volts 8 C.P., 55 Volts.

STANDARD EDISON LAMPS, 1881-1884.
The 16 C.P. lamp was called the "A" lamp and the 8 C.P. the "B"
lamp, the latter burned two in series on 110 volts. The construction
of the lamps as pictured above was standard from 1881 to 1884.

Two sizes of lamps were now being made, 16 candle-power
for 110 volts and 8 candle-power for 55 volts, the latter to
be burned two in series on 110 volts. The former was
called the "A" lamp and the latter the "B" lamp. The
A lamps were made "eight to the horse power," the term
watts not being in use at that time; the lamps therefore
consumed a little over 93 watts. They were rated to give
600 hours Hfe in service, but in the latter part of 1881 the
efficiency was increased, the lamps then being made ten to
the horse power, rated to give 600 hours life on circuits hav-
ing good voltage regulation.

65

THE INCANDESCENT LAMP

Development of Other Parts of Edison s System

In addition to lamps and dynamos, other parts of
Edison's incandescent electric lighting s^^stem had to be
invented, developed and manufactured to make the
system complete.

In order to protect the dynamos from accidental over-
load, such as a short circuit, an automatic device had
to be developed to disconnect them from the circuit.

LEAD WIRE FUSE, 1880
Edison invented the fuse which is universally used. Photograph,
courtesy of the New York Edison Company.

Edison invented the well-known lead wire fuse for which he
obtained a patent in May, 1880. The same type of fuse
was also used to protect the main circuit from troubles on
individual branch circuits, so that current would be cut off
only from the branch circuit where the trouble occurred.

66

THE INCANDESCENT LAMP

Lead made into short pieces of wire of various diameters
will carry current up to an amount determined by the size of
the wire. If the current is increased beyond that point, the
lead wire will be heated appreciably and finally melt. If the
current suddenly becomes very great, due to a short circuit,
the lead wire will melt instantaneously, thereby autompti-
cally opening the circuit before any damage is done.

The^demand for sockets, switches, fixtures, etc., became
so great that a separate organization was formed, known as
Bergmann & Company, which obtained a factory at 108

"t^,

3>'

EDISOA_MACHiNrwoll"''...;,

piMif liiinnni}

EDISON MACHINE WORKS, ISSl.
This factory was located on Goerck Street, New York City, the
manufacture of dynamos being shifted to it in 1881. In 1886, the
Works were moved to Schenectady, N. Y.

Wooster Street, New York, and started manufacturing early
in 1880. The capacity of this factory was soon outgrown
and in 1882 the plant was moved to a building on the corner
of Avenue B and 17th Street.

As there was insufficient space at the Menlo Park Labo-
ratory machine shop, another separate company was organ-
ized, known as the Edison Machine Works. A factory
building at Goerck Street, New York City, was obtained

67

THE INCANDESCENT LAMP

and the manufacture of dynamos was started there early in
1881. The capacity of this factory was soon overtaxed and
in 1886, the Works were moved to Schenectady, New York.
Edison felt that the wires supplying current from a
central station to the various buildings should be under-
ground. This necessitated the design and development of
a complete water tight and insulated underground method
of distribution, something that had never been previously
done; in fact it was considered impossible to prevent cur-
rent from Icavinc: the wires and being diverted from one

^■NPy

EDISONS ELECTRuLYTiC METER, 1882
This registered the amount of current used. Two chemically pure
pieces of zinc were put into a glass jar containing a solution of zinc
chloride. Current flowing from one zinc to the other through the
solution caused particles of zinc to be transferred from one to the
other. The amount of current used was measured by the loss of
one and gain of the other. This meter, a double one, is in the his-
torical collection of the Edison Pioneers by whose courtesy this
photograph is reproduced.

part of the system, through the earth, to another part of
the system, instead of being supplied to the lamps in the
buildings. He finally developed a complete system of under-
ground tubing, joints, junction boxes, branches, etc. These
were made by a subsidiary organization, the Electric Tube
Company, which obtained a factory at 65 Washington
Street, New York.

68

THE INCANDESCENT LAMP

It was also necessary to design a meter to register the
amount of current used by each customer as a basis for
bills to be rendered for the service given. An electrolytic
meter was finally evolved and in service was found to be
extremely accurate.

This meter consisted of a glass jar containing a solution
of zinc sulphate and two pieces of chemically pure zinc.
Direct current flowing through this cell would cause

EDISON'S JUMBO DYNAMO, 18S2
This dynamo had a capacity of 1200 lamps and was directly connected
to a steam engine. It is one of the original machines of the Pearl
Street Station of the Edison Electric Illuminating Company, now
the New York Edison Company, by whose courtesy the photo-
graph is reproduced.

particles of zinc to be transferred through the solution from
one zinc terminal to the other, the amount being in pro-
portion to the current flowing and to the length of time. Thus
one piece of zinc loses and the other gains in weight. This
difference measures the total quantity of current in ampere-
hours used, which, if multiplied by the voltage, would give

69

THE INCANDESCENT LAMP

the quantity in the modern term of watt-hours. The
voltage being approximately constant, the ampere-hours
were a direct measure for a basis of rendering bills on the
amount of electricity used. Actually only part of the total
current used was shunted through the cell so that the zinc
electrodes would not have to be inconveniently large in size.

MODEL OF PEARL STREET STATION
This was the first permanent central station in the world, starting
operations on September 4, 1882. Photograph by courtesy of the
New York Edison Company.

In 1880, Edison decided to build a large dynamo capable
of being directly connected to a steam engine instead of being
belt driven. Up to this time the dynamos he had made had
a capacity of sixty lamps, which in the present terminology
would be rated at six kilowatts (about eight horse power).

70

THE INCANDESCENT LAMP

A central station of even reasonable capacity would have
to have a vast number of these six kilowatt dynamos,
requiring a very large space and great investment. In order
to deliver 110 volts they had to be run at high speed,
about a thousand revolutions per minute, far beyond
that possible with a steam engine. It was, therefore, no
small matter to design a large dynamo to be directly
connected to a steam engine whose maximum speed at that
time was about one hundred revolutions per minute.

Edison was finally able to get an engine maker to make
a steam engine of about 120 horse power to run at 350 revo-
lutions per minute and then he made a dynamo of 1200 lamp
capacity to be directly connected to this machine. At this
time lamps were being made ten to the horse power, each
consuming about 75 watts. This 1200-light dynamo there-
fore had a capacity of 90 kilowatts (about 120 horse power)
and was nicknamed the "Jumbo" dynamo after the well-
known elephant, then the largest in captivity.

Edison had always believed that the most economical
method of supplying current for incandescent lamps was
by the generation of current in a large central plant instead
of by individual plants. In the latter part of 1880, plans
were started for a central lighting station in New York City,
and the first central station, the Edison Electric Illuminat-
ing Company of New York (now the New York Edison
Company) was incorporated in December, of that year.

The construction of the power plant, the more than four-
teen miles of underground mains, covering an area of about
one-sixth of a square mile between Spruce Street, Ferry
Street and Peck Slip on the north, the East River on the
east, Wall Street on the south, and Nassau Street on the
west, and the wiring of consumers' premises, took nearly two
years of work. Finally, on September 4, 1882, the Edison
Electric Illuminating Company of New York started
operations with a load of about 300 amperes supplying
about 59 customers having a total of 1284 sockets. It had six
Jumbo dynamos with a rated capacity of 7200 lamps, or
about 540 kilowatts (720 horse power). The station was

71

THE INCANDESCENT LAMP

located at 257 Pearl Street, New York, and its design was
quite equal to that of a modern plant. Real estate was so
expensive that in order to save space the boilers were located
on the ground floor and the dynamos and engines on the
second floor. On the top floor was a test rack with sockets
for a thousand lamps which was used to test out the station
before it was put into regular operation. The great weight
of the dynamos and engines on the second floor was sup-
ported b}^ special steel beams.

TJie TJiree-ii'ire System

Further study of the central station showed that the
amount of copper required in the mains to distribute the
current would have to be very great if the distance and
amount of current used was large. The investment for such
a great amount of copper would be very heavy, almost
prohibitive. After much thought, Edison evolved the
"three-wire" system of distribution which resulted in a
saving of 60 per cent of the amount of copper required by
his former two-wire system.

In the three-wire system, two 110-volt dynamos are
connected in series to give 220 volts. The circuit consists
of three wires, two connected to the outside wires of the
dynamos so that the voltage between them is 220 volts.
The third wire, called the neutral wire, is connected to the
connection between the two dynamos and runs wherever
the outside wires run. The voltage between the neutral
wire and either outside wire is 110 volts, and all lamps are
connected between the neutral wire and one or the other of
the outside wires, the load being about evenly divided. It
is good practice to make motors for 220 volts and connect
them to the outside wires, as this preserves the balance
between the two sides. A 110-volt motor on one side dis-
turbs the balance a great deal.

The current flowing through the outside wires of a
three-wire distributing system, provided the lamps are
evenly divided, is half that which flows through the wires
of a two-wire system having the same aggregate number of

72

THE INCANDESCENT LAMP

lamps. As the amount of power lost in these wires is
equal to the square of the current flowing in them times
their resistance (the C-R loss), the resistance of the outside
wires can be quadrupled for the . same loss (the current
1 )eing halved) by making them one-quarter the size of those
used in a two-wire system. Therefore, if the load were
equally balanced at all times on each side of a three-wire

w

DIAGRAM OF EDISON S THREE-WIRE SYSTEM, 1882
This system reduced the amount of copper necessary in his former
two-wire distributing system by 60 per cent

system, the neutral distributing wire could be dispensed
with, making a theoretical saving of 75 per cent in copper.
In practice there are, however, at one time or another,
more lamps burning on one side of the system than the
other, so that a neutral distributing wire becomes neces-
sar}^ Even so, it is possible to obtain a 60 per cent saving
in copper. Edison obtained a patent on the three-wire
system early in 1883.

This system is now universally used where direct current
is distributed, and is largely used on alternating-current
local distributing systems. Its invention has caused the

73

THE INCANDESCENT LAMP

saving of untold millions of dollars of investment and it is
probable that without it the central station industry
would have been retarded for many years; at least until the
alternating-current high voltage distributing system had
been established.

74

CHAPTER THREE
Development of Filaments

In an incandescent lamp the current passing through the
resistance of the filament heats it to an almost white heat
and in this condition it radiates light. The hotter it is
heated the more Hght it radiates; also the hotter it is
heated the sooner it wears out. Edison decided that to be
satisfactory a lamp should last 600 hours, so lamps were
rated to operate at a temperature at which the filament
would last 600 hours. As filaments were improved in
quality the operating temperature was raised in such pro-
portion that there would be no change in life. Each
increase in filament temperature improved the efficiency
of the lamp, causing it to give more light for each unit of
electricity used, so from the beginning it has been the
endeavor to improve the filament so that it could be safely
operated at higher temperature.

The Carbon Filament

For about 26 years all incandescent lamps had carbon
filaments made by carbonizing cellulose — paper, bamboo or
cotton. All cellulose is composed largely of carbon com-
bined with other elements, principally hydrogen and
oxygen. When cellulose is slowly heated in a closed furnace,
away from air, it is decomposed, the hydrogen and oxygen
and some of the carbon is driven out and the carbon skele-
ton remains. This carbon skeleton is the filament. It is
very dense and hard and much like anthracite coal.

Edison's first commercial lamps had a filament of car-
bonized paper which was rather porous and fragile. When
the lamp factory was started in 1880, the lamps were made
with filaments of carbonized bamboo which was very hard
and strong. Much had to be learned about carbonizing

75

THE INCANDESCENT LAMP

bamboo, it shrinks from 20 to 30 per cent during the
process, and it must be free to shrink but must not be
allowed to distort. If the shrinkage is too much restrained,
weaknesses in the filament will result. The atmosphere sur-
rounding the filament during the carbonizing and cooHng
must be a reducing atmosphere, free from air. The tem-
perature of the carbonization, especially when the decom-

CARBOXIZING FURANCES

position of the cellulose is going on, must be very slowly
raised or the filaments will be stuck together because of too
rapid distillation of the hydro-carbons. After reaching 600
deg. F. the temperature may be rapidly increased until the
crucibles are white hot. As the crucibles containing the
filaments cool down they must be surrounded by a reducing
gas to prevent air reaching the filaments.

Edison sent several men all over the world to get samples
of different bamboos. In the summer of 1880, William H.

76

THE INCANDESCENT LAMP

Moore went to China and Japan. He sent great bales of
samples to Menlo Park and after careful tests, a certain
variety and growth of Japanese bamboo called "Madake"
was found to be the best. Moore was instructed to arrange
for the cultivation and shipment of this, so he got a Japanese
farmer to do it. The farmer displayed such ingenuity in
fertilizing and cross fertilization that the product was
constantly improved. It was used until 1894.

In December, 1880, John C. Brauner was sent to South
America. He travelled over two thousand miles on foot
and by canoe in the wilds of southern Brazil and secured
a great variety of specimens of bamboo. None, however,
was found to be superior to the Japanese bamboo then being
used.

Another expedition was sent to Cuba and Jamaica, the
trip taking two months. Three men explored the Florida
swamps for five months. None, however, found samples
as good as the Japanese variety.

A few years later (1887) two men, Frank McGowan
and C. F. Hanington, went to Brazil and up the Amazon
River for 2300 miles. There the two separated, McGowan
exploring Peru, Ecuador and Colombia, Hanington went
down the Amazon River again, up the La Plata River and
through Uruguay, Argentine and Paraguay. McGowan's
trip was particularly dangerous as he went through a
comparatively wild and unknown country filled with
hostile natives.

The last trip of this kind was made by James Ricalton
who went completely around the world, the trip taking
exactly one year. He was unable, however, to find a fiber
better than that being obtained from Japan.

Clamps

Prior to 1881 the filament was fastened to the leading-in
wires by delicate clamps. This is why the joint between
the filament and leading-in wire is often called the clamp.
From 1881 to 1886, this connection between the filament
and the leading-in wire was copperplated. To keep the

77

THE INCANDESCENT LAMP

copper from being melted by the hot filament the ends of the
latter were made large enough to radiate the heat and so
keep the temperature down. The filaments were cut with
these large ends on them ; this increased the expense and
trouble of making them and prevented any adjustment of
length after they were cut .

Differences in dimensions due to shrinkage or cutting
inaccuracies made these filaments quite different in voltage,
so that in any lot of lamps made, the voltage of individual

FILAMENT
CLAMPS, ]880
The filament was orig-
inally fastened to the
leading-in wires by del-
icate clamps.

COPPERPLATED
CLAMPS, 1881
From 1881 to 1886 the con-
nection between the filament
and leading-in wires was
made by copperplating them
together.

CARBON PASTE

CLAMPS. 1886

A carbon paste was used

to fasten the leading in

wires to the filament.

lamps would vary 15 or 20 per cent. To utilize these lamps,
electric lighting plants were arranged to be operated at
different voltages. Plants operating all the way from 95 to
125 volts were thus established all because it was impossible
to make all the lamps of the desired voltage which was 110.
About 1886 carbon paste was adopted for making the
connection between the filament and the leading-in wire.
Since this paste joint would not melt or be injured by the
hot filament, enlarged ends were no longer necessary on the
filaments. This reduced the cost and simplified the manu-
facture of filaments, permitting any adjustment of their
length which was desirable after carbonization. Although
this somewhat reduced the variation in voltages of lamps

78

THE INCANDESCENT LAMP

made, the difference was still so considerable that each lamp
had to be photometered to determine its voltage at its
proper candle power.

The carbon paste used in these lamps was first made by
mixing graphite and india ink, and later by mixing graphite
with caramehzed sugar and gum arable. Paste for large size
filaments was made of graphite, soft coal and coal tar pitch.

TREATING CARBON FILAMENTS, 1S93
The carbon filament was materially improved by coating it with
graphite. This was done by heating the filament by passing cur-
rent through it for a few seconds in gasoline vapor.

The joints containing pitch were heated red hot before
sealing the filament in the bulb to reduce the pasted joint
to coke.

Treated Carbon Filaments

For over ten years the filaments used in all Edison
lamps were carbonized bamboo. Other lamp manufacturers
used an additional process called "treating" which was
patented by Sawyer and Man. In this treating operation
the filaments were held by clamps in a bottle which was

79

THE INCANDESCENT LAMP

connected on one side to a vacuum pump and on the other
to a bottle containing gasoline. The vacuum pump first
drew the air out of the bottle containing the filament
and then drew gasoline vapor into it. Electric current
was then passed through the filament, heating it to
a very high temperature, the gasoline vapor in contact
with the filament was decomposed and a layer of graphitic
carbon was deposited on the filament. This process was
capable of nice adjustment and gave the filament just the
resistance desired. The graphitic coating also gave the
filament a much better light radiating characteristic and
consider ably reduced the variation of voltages in the lamps .
This patent expired in 1893 and after that Edison lamp
filaments were so treated.

Later an automatic treating machine was developed by
John W. Howell. In this machine the operator made no
adjustments, only putting filaments in the bottle and taking
them out. With this machine the gasoHne was held in an
underground tank outside the building, pipes bringing only
the gasoline vapor indoors. Thus the danger of fire was
removed, which was always present when each operator
had a two-quart bottle of gasoline on the table beside her,
as was previously the case.

The quality of the treated carbon filament depended
upon the amount of gasoline vapor in the bottle and the
temperature of the filament during treating. The amount
of vapor in the bottle was measured by a "dose" bottle
which was connected first to the vacuum pump, then to the
gasoline vapor supply which filled it with vapor, and then
to the treating bottle which had been exhausted of air and
into which the dose bottle emptied its dose of vapor. The
electric current was adjusted to maintain the filament at an
approximately constant temperature during the treating
operation, which required about 3}/2 seconds. During this
time the resistance of the filament was reduced to one-third
of its resistance before treating.

In this treating machine there were four treating bottles
which were used in regular order. Stoppers, through which

80

THE INCANDESCENT LAMP

extended clamps which held the filaments and connected
them to the electric current, fitted the bottles. When a fila-
ment was placed in a bottle, the latter was connected to a
vacuum pump which pumped the air out of it. Then the
bottle was connected with the dose bottle which gave it the
correct amount of gasoline vapor. Electric current 'was then
passed through the filament, treating it to the proper resist-
ance, at which point the current was cut off by an automatic
device. Air was then admitted to the bottle, the filam.ent

SQUIRTING THE CELLULOSE CARBON FILAMENT, 1894
Cotton was dissolved in a hot zinc chloride solution, the syrup being
squirted through a die into alcohol to harden the thread formed.
This thread was then washed, dried, wound on forms to give it the
desired shape, cut ofF in bunches and carbonized.

taken out and a new filament put in its place. All this,
except putting the filament in the clamps and removing it,
was done automatically by means of two fiat rotary valves,
invented by Mr. Howell. He also invented the mechanism
which operated them.
Squirted Cellulose Carbon Filament

In the Spring of 1888, Leigh S. Powell, an EngHshman,
developed a process he had originated for preparing cellu-

81

THE INCANDESCENT LAMP

lose for filaments. Sir Joseph W. Swan had some time pre-
viously invented a process along very similar lines. The
two processes, although the same in principle, consisting
as they did of projection of a solution containing cellulose
through a nozzle into a setting liquid, were very different
as regards the materials needed and the operations and
apparatus employed.

In Swan's process nitro-cellulose (gun cotton) was dis-
solved in acetic acid. After squirting the solution through

■

TREATED SQUIRTED CELLULOSE CARBON LAMP. 1894
The lower specific resistance of this filament required that its length
be increased, the filament having a loop which was anchored to the
stem.

a small orifice into alcohol and washing the thread so formed,
it was necessary to denitrate the thread before it could be
carbonized. In Powell's process the danger of using and de-
nitrating the gun cotton was eliminated. Cotton was dis-
solved in a hot zinc chloride solution to form a syrup which
was squirted through a die into alcohol. The alcohol soHdified
the squirted thread and dissolved out some of the zinc chlo-
ride, the rest of the zinc chloride being washed out with several
changes of water. The thread was then wound on drums and

82

THE INCANDESCENT LAMP

dried. Itwasthena strong, smooth, round, structureless, cellu-
lose thread which was wound on forms to give it the desired
shape, cut off in bunches, packed in crucibles and carbonized.

With this squirted cellulose, filaments of any desired
length could be made, whereas with bamboo the length was
Hmited to the distance between the joints of the cane and
was not long enough for treated filaments of the desired
dimensions. The treated squirted cellulose oval anchored
filaments were the best carbon filaments ever made, their
commercial adoption in this country beginning about 1894.
Aggregate Improvement of the Carbon Filament

The lamps commercially sold in 1881 produced, when
new, 1.68 lumens per watt. Lumens per watt is the term
now used to express the efficiency of a lamp. A lumen is
the amount of light in a beam having a cross-section of
one square foot at a distance of one foot from a light source
of one candle power. If a light source of one spherical
candle power be placed at the center of a sphere of one foot
radius, it will give one lumen on each square foot of surface
of the sphere. As there are 12.57 square feet of surface on a
sphere of one foot radius, one spherical candle power will
give 12.57 lumens. Therefore, any light source will give
12.57 lumens for each spherical candle power; that is, the
number of lumens given by any lamp is 12.57 times its
spherical candle power. Carbon lamps were rated in
horizontal candle power and the ratio of their horizontal
candle power to their spherical candle power varied con-
siderably. To determine their lumens, their spherical
candle power must first be determined, which, multiplied
by 12.57, gives their lumens.

The efficiency of 1.68 lumens per watt was steadily
improved, first by improved methods of carbonizing and
exhausting, then by surfacing the filament with asphalt,
then by further improvements in vacuum production,
including the Malignani chemical exhaust, and finally by
the hydrocarbon treating process and the squirted cellulose
filament. These improvements cannot be separately valued,
but the carbon lamp of 1906, which is practically the same

83

THE INCANDESCENT LAMP

as the few now made, gave 3.4 lumens per watt. If the
1906 carbon lamp were burned at the same efficiency as
that of the lamp of 1881, it would last 139 times as long,
so it may be said that the quality of the 1906 lamp was 139
times better than that of the 1881 lamp.
The Gem or Metallized Carbon Filament

Dr. Willis R. Whitney, head of the Research Laboratory
of the General Electric Company at Schenectady, had
developed an electric resistance furnace. This consisted
of a carbon tube, about three inches in diameter, inside of
which articles to be heated could be placed. A heavy cur-
rent of several thousand amperes was passed through the
tube, heating it to a very high temperature, estimated to
be about 3500 deg. C, which is about 500 deg. below the
melting point of carbon and about 1650 deg. above the
operating temperature of the carbon filament.

To give an idea of the terrifically high temperature
reached by this electric furnace, the writer once looked
directly into the open end of one of the tubes when it was
fully heated and, when the eyes were adjusted to the task,
held a 50-volt carbon filament lamp directly between the
eye and the hot interior of the tube. The voltage on the
lamp was then slowly raised and, when the voltage on the
50-volt filament was over 100 volts, the filament looked
like a dark line on the background of the hot tube.

Dr. Whitney's original experiments were based on the
idea that previous carbon filaments still retained small traces
of such ash oxides as silica and alumina, substances which
are not readily reduced by carbon at lamp temperature.
It was evident that bulb blackening of carbon lamps might
be due to the reaction of heat on carbon dioxide by which
carbon monoxide and carbon are formed. The conditions
of a lamp were such that this carbon could be deposited on
the glass and the monoxide could react again with the fila-
ment to give more dioxide. In this way a steady blackening
of glass could proceed indefinitely. The application of
excessive temperatures to the filaments in vacuo could not
succeed in removing the ash oxide because the carbon

84

THE INCANDESCENT LAMP

would itself vaporize too much, but it was evident that the
filaments could not vaporize inside a highly heated carbon
tube, while the oxides would be reduced by such excessive
temperatures. The effect actually produced of changing
the nature of the graphite coating in the treated filament
was not anticipated.

The highest temperature reached during the time a
carbon filament is carbonized is about 2700 deg. and is,
therefore, considerably below that which Dr. Whitney was

ELECTRIC RESISTANCE FURNACE, 1905
Dr. W. R. Whitney invented the Gem lamp which had a carbon fila-
ment subjected to the high temperature of an electric resistance
furnace which he also invented. The Gem lamp was 25 per cent
more efficient than the regular carbon lamp.

able to obtain with his furnace. Having some filaments
on hand, he decided to try the experiment of heating these
already carbonized filaments to see if they could be im-
proved. After subjecting them to the high temperature,
he made them into lamps in his laboratory and Hfe tested
them. They gave surprisingly good results.

He ordered some filaments from Harrison to repeat the
experiment, but these failed to give good results. A second

85

THE INCANDESCENT LAMP

lot of filaments sent him were no better. Upon investiga-
tion it was found that he had thought that the filaments,
which he had on hand and which gave good results, were
untreated filaments, whereas they were really treated
filaments, so that he had ordered untreated filaments from
Harrison with which to repeat his experiments. He
thereupon obtained some treated filaments from Harrison
and this time he repeated his original success.

These treated filaments, after being subjected to the
high temperature of the electric furnace, were very much
blistered, as if gases had come out from within the filament.
It was found that these blisters disappeared if the untreated
filament were first heated in the electric furnace, then
treated and then again heated in the furnace. A lamp with
this filament was developed and called the Gem or metal-
Hzed carbon filament lamp and was put on the market in
1905. Dr. Whitney obtained a patent on it in March, 1909,
the original application for which was made in February,
1904. It was operated at 25 per cent higher efficiency than
the regular carbon lamp, or 4.25 lumens per watt for the Gem
compared with 3.40 for the regular carbon lamp. The same
life results (600 hours) were obtained with both lamps.
If the Gem lamp were operated at the same efficiency as
the regular carbon lamp, it would last 4^ times as long,
hence, its quality may be said to be 4% times as good.

The resistance characteristic of an ordinary treated
carbon filament is "negative," that is, its resistance
decreases with increases in temperature. Metals have a
"positive" characteristic and the resistance of the Gem
filament increases with increases in temperature, similar to
that of metals. This is why the new filament was called
the metallized carbon or Gem (General Electric Metallized)
filament.

The chief change in the physical properties of the Gem
compared with the carbon filament, which made it possible
to operate it safely at a higher temperature (about 1900
deg. C.) and so give a greater efficiency, was the change in
the treated coating of the filament which is called the

86

THE INCANDESCENT LAMP

"shell." This shell is graphite, both before and after firing
in the electric furnace, as has been determined by chemical
test. Furthermore, it has the greasy feel of graphite and
gives the characteristic pencil mark of graphite on white
paper. The shell after firing is a purer graphite, as its
specific gravity is much higher and it is much tougher and
more flexible than before. The shell can be pulled off the
core (the base filament) in short tubular sections. This fired
shell, if pressed flat, will spring back to its original form
when the pressure is removed, whereas the unfired shell
will break with very little pressure. The unfired shell
has a negative resistance characteristic up to a certain
temperature, after which it has a slightly positive charac-
teristic. The fired shell has a much lower cold resistance
and a decidedly positive characteristic at all temperatures.

Firing the core drives out most of its mineral ash
constituents and so prevents blistering of the finished
filament. The ash content is more volatile than carbon.
This ash content (as well as the carbon of the filament)
vaporizes in an ordinary carbon lamp during its burning
life, condensing on the bulb, and forms part of the discolora-
tion on the bulb. Owing to the small amount of ash present
in the Gem filament the lamp maintains its candle power
during life much better than the regular carbon lamp, due to
the lesser blackening of the bulb. The untreated carbon
filament is shiny black, the treated carbon is shiny gray and
the Gem filament is dull gray in color. By this means it is
possible to distinguish these lamps from one another.

The first Gem lamps for 110-volt service, put on the
market in 1905, had two single hairpin filaments connected
in series. Later it became possible to make Gem lamps
having a single oval filament for use on 110 volts, these
being put on the market in 1909. Lamps were made in
sizes from 30 to 250 watts but, with the introduction of the
tungsten filament lamp in 1907, the higher wattage sizes
soon disappeared from use. The 50-watt lamp was the
most popular size and was marketed until 1918, when the
manufacture of all Gem lamps ceased.

87

THE INCANDESCENT LAMP

Gem series lamps were made for street lighting but
they also quickly disappeared, as did the 30- and 60-volt
Gem lamps for train Hghting service, with the advent
of the tungsten filament. Gem lamps for 220- volt service
were not manufactured.

The Osmium Filament

Dr. Carl Auer Von Welsbach, who had produced the
Welsbach gas mantle, invented the first commercial metal
filament lamp, the Osmium lamp, but it was used only in
Europe and in very limited quantities.

^T^.. T A ATT, inn- <^EM LAMP. 1909

GEM LAMP, 190o . innn-^i 11

^, , . -,,^ , In 1909 it became possible

The lamp for ^110-volt ^^ ^^^^ ^ 3i„g,g ^^.^y ^j.

service originally Jhad ament for 110-volt ser-
two hairpm filaments ^ice. Gem lamps dis-
connected m series, appeared from the

market in 1918.

Osmium is an extremely rare and expensive metal,
costing much more than platinum, which itself is over five
times as expensive as gold. It is non-ductile and exceed-
ingly brittle and so cannot be drawn into wire. Von Wels-
bach applied in this country in August, 1898, for patents
on the lamp and processes for making the filament, the
patents being granted in November, 1910. The filament

88

THE INCANDESCENT LAMP

was made by mixing powdered osmium with a binder, such
as syrup of sugar, the resulting paste being squirted by
pressure through a die. The thread formed was heated to
carbonize the binder and current then passed through it in
moist hydrogen gas. The current heated the thread to a
high temperature which decomposed the water vapor, the
oxygen of which combined with the carbon binder forming
carbonic acid gas. The particles of osmium remaining
were then sintered together by the high temperature, form-
ing the filament.

OSMIUM LAMP, 1S99-J906.
A few of these lamps were made in Europe. They were considerably
more efficient than the carbon lamp, but on account of the scarcity
of osmium, the filament material, it was impossible to make them
in large quantities.

The filament was extremely fragile and, as its resistance
was very low, at first only low voltage lamps were made
to burn tw^o or more in series on 110-volt circuits. Later a
few 110-volt lamps were made. Osmium melts at about
2500 deg. C, which is much below the melting point of
carbon, but the filament can be operated at a higher tem-
perature than that permissible w^ith carbon for the same life,
as it does not vaporize so easily. This made it possible to
operate the lamp at 5.9 kimens per watt, which is about 75
per cent more efficient than the carbon lamp.

89

THE INCANDESCENT LAMP

This extremely high (at that time) efficiency lamp was a
tremendous improvement, and even with its fragility, would
have formed a great step forward in the lamp art if it could
have been produced in large quantities. The world was ran-
sacked for osmium. Expeditions were sent out to explore
wild territory, engineers being hired to go out with pack
mules to traverse unknown country far away from places
man had ever visited. Even as late as the summer of 1903,
the Canadian Northwest was being explored, but with all
these efforts and expenditures, the best that could be done
was to obtain but a small quantity of the rare metal.

A few thousand lamps were made, and these were gen-
erally not sold, but rented so that the burned out lamps
could be obtained to recover the osmium left in them.
They were put on the market about 1899, and only used in a
few installations in Berlin and Vienna, where the lamps were
made. Manufacture of the lamp was abandoned in 1906,
when the tungsten lamp appeared. Osmium lamps were
not marketed in this country.
The Tantalum Filament

The metallic substance, known as tantalum, one of the
elements, was discovered over a hundred years ago, about
1802. It is practically unaffected by various chemicals,
an early writer stating that "even when in the midst of an
acid it is unable to take the liquid unto itself." It was
named after the fabled Tantalus, who was condemned to
stand up to his chin in water which constantly eluded his
lips when he attempted to quench his tormenting thirst.

Dr. Werner Von Bolton, a Russian chemist, in the
employ of the Siemens & Halske Company, a large elec-
trical manufacturer in Germany, discovered, about 1902,
that this metallic substance really contained a considerable
amount of oxide of tantalum. He removed the oxide in
the metal by placing some of it between the poles of an
electric arc in vacuum, a vacuum pump removing the oxy-
gen as fast as it was released. He later found that at first
he did not obtain pure tantalum because what he got was
an extremely hard metal, so hard that it was impossible

90

THE INCANDESCENT LAMP

for a diamond drill rotating 5000 times a minute for
three days to drill a hole through a sheet of it only
one millimeter thick. This extreme hardness was due to
impurities which disappeared when he employed electrodes
of the first lot of tantalum he made. The pure metal,
however, is still hard, about equal to that of the hardest
steel, but it is ductile so that it can be drawn out into a fine
wire, having a tensile strength of about 100,000 lb. per
sq. in.

TANTALUM LAMP, 1906

This lamp had a filament of the metal tantalum, and was much more

efficient than the carbon lamp. It disappeared from use in 1913.

Tantalum is about twice as heavy as iron, having a
specific gravity of 14.5, that is, it is 143^ times as heavy as
distilled water at ordinary temperature. Its melting tem-
perature is high, about 2850 deg. C, but while this is con-
siderably below that of carbon. Dr. Von Bolton found that
it could be operated as a lamp filament at somewhat higher
temperature than that permissible with the Gem lamp
for the same life because it vaporized less easily. This
made it possible for him to produce a tantalum lamp to
poerate at 4.8 lumens per watt. It had a quahty value

91

THE INCANDESCENT LAMP

nearly 2^ times that of the Gem lamp and if the two were
operated at the same efficiency, the tantalum lamp would
live 2.71 times as long as the Gem lamp. Dr. Von Bolton
applied for a U. S. patent in May, 1902, which was granted
in April, 1906.

Tantalum has a relatively low electrical resistance, so
the filament for a 110-volt lamp had to be long and thin.
The 44-watt lamp originally made had a wire filament
1.8 thousandths of an inch in diameter and about twenty
inches long. For comparison the 50-watt carbon lamp
filament is four thousandths of an inch in diameter and
about nine inches long. A human hair is about three thou-
sandths of an inch in diameter.

The tantalum lamp was put on the market in this
country in 1906. The original 44-watt lamp was later
changed to 40 watts, and an 80-watt lamp added for 110-
volt circuits. It was also supplied in round bulbs, and
lamps for 30-, 60- and 220-volt service were also made.
It was found that while good life results were obtained on
direct -current circuits, the filament, when burned on
alternating current, rapidly crystallized and so did not last
long. As direct current is supplied by Hghting companies
in only a few cities, the use of the lamp was limited, the
greater portion of electric current supplied being alternating.
The lamp disappeared from the market in 1913.

The Tungsten Filament

The metal tungsten, an element, was discovered in
1781, and for more than a century and a quarter was known
to chemists as an entirely intractable metal, existing only
as a powder of hard, brittle particles or as a rough, more or
less fused mass, incapable of being forged or worked in
any way. It was used only in alloys, notably in tungsten
steel, making the steel extremely hard, and as a con-
stituent of chemical compounds.

It is extremely heavy, nearly twice as heavy as lead.
It is now known to have a specific gravity of 19.1; prior
to its use as a filament, authorities stated it to be from about

92

THE INCANDESCENT LAMP

17.2 to 17.6. It has a melting temperature of about 3400
deg. C, a temperature at which asbestos and fire brick
would melt like wax in a furnace. But little of the proper-
ties of the metal itself were known until it was used in a
lamp, one authority even stating as late as 1903, that its
melting temperature was 1500 deg. The operating tem-
perature of a treated carbon filament is about 350 deg.
higher than this.

The name tungsten is derived from the Swedish
"Tung" meaning heavy and "Sten" meaning stone.
Its chemical symbol " W" is derived from Wolff, one of the
early experimenters on the metal.

Tungsten is plentiful, being obtained from various
ores, such as Wolframite, a tungstate of iron and manganese,
and Sheelite, a tungstate of calcium. Ores are mined in
Colorado, California, New Mexico, China, Korea, and many
other places. The ore is usually purified to the oxide,
which is a yellow powder resembling sulphur. There are
lower oxides which are bluish and brown. The oxides are
further reduced to tungsten, which appears as a fine gray-
black powder.

Early Suggested Uses of Tungsten in Incandescent Lamps

As a matter of record it is interesting to note that
Turner D. Bottome, an American, applied for a patent in
September, 1887 (granted in April, 1889), which discloses a
process consisting of saturating carbon filaments with a
solution containing a tungsten compound, baking the fila-
ments and reducing the tungsten compound to tungsten
metal. This process was to be repeated as often as neces-
sary in order to obtain the proper amount of tungsten in
the carbon filament. Bottome's idea was that by adding
tungsten to the carbon it would produce an additional
hardness to the filament such as is conferred upon steel by
the addition of tungsten. The scheme was never used.
Such a filament, if operated above the normal temperature
of the carbon lamp, would rapidly blacken the bulb with a
deposit of carbon.

93

THE INCANDESCENT LAMP

Alexandre De Lodyguine, a Russian, suggested the use
of tungsten and other materials to make up a composite fila-
ment in patents he applied for in 1893 and 1894. At this
time Edison's basic carbon lamp patent had been sustained
in the courts, and the Westinghouse Company was trying
to develop a lamp that would not infringe this patent.
De Lod^'-guine was retained by the Westinghouse Company
to do this, and put in two years of intensive work but with-
out success.

De Lodyguine 's idea was to build up a high resistance
coating or shell on a platinum or carbon core, thereby
making a high resistance composite filament. The shell
could consist of molybdenum, tungsten, rhodium, iridium,
ruthenium, osmium or chromium. The scheme was never
used, as with a platinum core, the platinum would melt,
soak through the shell and vaporize quickly, blackening
the bulb if it were operated above the filament temperature
of a carbon lamp. Platinum melts about a hundred degrees
below the operating temperature of the carbon lamp. With
a carbon core the same difficulty would occur as in Bot-
tome's scheme.

Invention of the Tungsten Filament Lamp

Alexander Just and Franz Hanaman, in 1902, were
laboratory assistants to the professor of chemistry in the
Technical High School in Vienna. Just was making use
of his spare time by working in another laboratory trying
to develop an incandescent lamp having a filament of
boron. His means were very limited, his whole income
being about $55 per month. In August, 1902, he got his
co-worker Hanaman, whose monthly income was even less,
to assist him. The two conceived the idea of trying to
produce a tungsten filament lamp and they worked on
both the boron and tungsten lamps for about two years.
The boron lamp was a failure.

They first started experiments on the tungsten lamp
by exposing a carbon filament at high temperature to the
vapor of tungsten oxychloride in the presence of a small

94

THE INCANDESCENT LAMP

quantity of hydrogen. Their theory was that a complex
chemical reaction takes place, depositing the tungsten
of the oxychloride in place of the carbon, and that this
reaction continues until the carbon of the filament has
been entirely replaced by tungsten.

Their aim was to make a pure tungsten filament and,
as they knew that tungsten was brittle and unworkable
so that it could not be drawn out into a wire, they thought
this carbon replacement method would finally produce a
tungsten filament. This effort was a failure for the reason
that the first thin coating of tungsten on the carbon filament
prevents further action between the carbon and tung-
sten oxychloride vapor. This filament merely became
one having a carbon core and a tungsten shell, and when
operated at a temperature above that of the ordinary
carbon lamp, the carbon would dissolve through the
tungsten, vaporize, and quickly blacken the bulb, as in
Bottome's scheme.

They were usinga paste containing graphite and a binding
material, such as coal tar, to fasten the filament to the
leading-in wires. They found that much of the black
deposit in the bulb came from this paste, so they heated
the pasted joints in hydrogen gas and found that the
blackening was very materially reduced. This led them
to believe that there must be some de-carbonizing process
going on. Being chemists they came to the conclusion
that some oxidizing substance was acting as a go-between
between the carbon and hydrogen. The hydrogen gas they
obtained was produced by the action of hydrochloric acid
and zinc, and they found that it contained a considerable
amount of water vapor. They therefore reasoned that the
high temperature decomposed the water vapor, the oxygen
combining with the carbon.

Finally they evolved a process of making a substan-
tially pure tungsten filament by coating a fine carbon
filament with tungsten deposited by heating the carbon
filament in a vapor of tungsten oxychloride as previously
described. The coated filament was then heated to a

95

THE INCANDESCENT LAMP

high temperature by passing current through it in an
atmosphere of neutral gases which would not react on
it chemically. This heating made the carbon core dis-
solve into the tungsten shell surrounding it, the car-
bon then being removed by another heating in an
atmosphere of water vapor and hydrogen. Later the
first heating was dispensed with, the second heating
accomplishing the results obtained by the original first
heating.

Another process was evolved by them, which was
commercially used in this country for several years. It
produced what was called the "pressed" filament and
consisted of mixing tungsten powder with an organic
binding material, of which there are several that can
be used. In the commercial process, a very fine grained
tungsten powder was mixed with a solution of sugar and gum
arable to make a thick paste. This paste was squirted
under high pressure through a diamond die and caught in
loops on a piece of cardboard. Tungsten is so hard that it
will soon wear out any other than a diamond die. The loops
were baked enough to partly carbonize the binder and then
were passed through a "forming" machine in which electric
current of increasing amount was passed through them
while they were in an atmosphere of hydrogen and nitro-
gen which contained some moisture. This removed the
binder and left substantially pure tungsten in the fila-
ments.

Just and Hanaman found that the substantially
pure tungsten filament they were able to make could
be operated at about 7% lumens per watt and yet give
good life results. This was an enormous improvement
over all previous lamps made. Their financial resources
by this time were so depleted that they did not have
sufficient money to apply for patents to protect their
invention in all the various European countries. They
finally were able to borrow $60 from a chemical manu-
facturer in Vienna with which to apply for British and
French patents, which were filed on Nov. 4, 1904.

96

THE INCANDESCENT LAMP

They found it difficult to obtain financial assistance
to develop their invention further, but they finally
induced a carbon lamp manufacturer in Ujpest, Hun-
gary, to try out their lamp. Much further experimental
work had to be done before the lamp could be produced
commercially, the lamps being put on the market in
Europe in limited quantities in September, 1906. They
used the carbon filament displacement method at first,
later the pressed filament. In July, 1905, they appHed
for a patent in this country.

MULTIPLE TUNGSTEN FILAMENT LAMP, 1907

This lamp was originally nearly three times as efficient as the carbon

lamp.

The General Electric Company bought Just and Hana-
man's American patent rights and after much develop-
ment work, marketed, early in 1907, a street series and
100- volt multiple lamp. The filament was rather fragile
and the lamps had to be handled carefully. Notwith-
standing the fragility, their high efficiency made them
a great commercial success, the tungsten filament making
the greatest advance ever made in the quality value
of the vacuum incandescent lamp. If the 100-watt,

97

THE INCANDESCENT LAMP

110-volt tungsten lamp of 1907, having an efficiency
of 7.85 lumens per watt, were operated at the same
efficiency as that of the tantalum lamp, it would
last 27.1 times as long, making its advance over the
tantalum lamp just ten times the advance of the
tantalum over the Gem lamp. Nearly half a million
tungsten filament lamps were sold during the first year,
1907.

Tungsten has a low electrical resistance, lower than
tantalum, about half that of platinum and very much
lower than that of carbon. However, when heated, tung-
sten increases greatl}^ in resistance and even though the
carbon filament decreases in resistance when heated, the
tungsten filament in a lamp must be much longer and
thinner than that in a carbon lamp. The 40-watt, 110-volt
vacuum tungsten filament lamp has a filament very nearly
two feet long and about 1.6 thousandths of an inch in
diameter. In order to get this long tungsten filament
in a bulb, several hairpin loops of the pressed tungsten
filaments were mounted on a spider, and connected in series
with each other to get the requisite resistance for 110-volt
circuits.

Series lamps were also put on the market which quickly
displaced the carbon and Gem lamps used in street Hghting.
They not only consumed less energy for the same candle
power given by the other lamps, but made it possible to
greatly increase the lamp capacity of the constant current
transformers used. As a result, larger sizes and greater
numbers of street lights began to be used.

The low resistance of tungsten made lower voltage
lamps commercially feasible, so that in lighting trains
30- and 60-volt tungsten lamps immediately displaced
the lamps formerh^ used. The lighting of automobiles
with 6- volt lamps operating on storage batteries soon
replaced the oil and acetylene lamps formerly used.
Flashlights received a tremendous boom, as the 2}^- and
3 3^- volt tungsten filament lamps tripled the capacity of
the small dry batteries used.

98

THE INCANDESCENT LAMP

Tiiugsteji Lamp Patent Granted to Just and Hanaman

There were two other inventors, who had appHed before
Just and Hanaman, to the Patent Office in Washington
for patents covering a tungsten lamp filament. One was
Von Bolton, the inventor of the tantahim lamp, whose
appUcation was dated November 10, 1904, and the other
was Dr. Hanz Kuzel, a German, who applied January 4,
1905. Just and Hanaman filed their application on Julv 6,
1905.

Von Bolton's application covered various metals,
among which tungsten was mentioned, which were to be
melted and could be fashioned into filaments by a drawing
process. He had discovered that the supposedly non-
ductile metal tantalum, if purified, became ductile and
could be drawn into a wire and would make a good lamp
filament. He did not know that any other metal would
make a good lamp filament, but there was a large group
of metals whose properties were little known and whose
adaptability to the lamp art was not even known at all.
He appears to have thought that possibly some of these
other metals might be made ductile if purified and thus
make good lamp filaments and to have wondered if his suc-
cess with tantalum might not be repeated with some other
metal by some other inventor. Desirous of forestalling such
other inventor. Von Bolton filed his speculative patent
application.

Up to this time it had been impossible to produce
ductile tungsten so that it could be drawn into a wire
by any known process. The Patent Office, therefore, ques-
tioned the operativeness of Von Bolton's application. As
will be shown, a brilliant invention was later made by
another inventor by which tungsten could be drawu into a
wire by an entirely new process. This new process was
not covered by Von Bolton's application.

The vSiemens & Halske Company, Von Bolton's em-
ployer, had in 1903 abandoned his theory of the ability
.to draw tungsten. They had, in that year, obtained an

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THE INCANDESCENT LAMP

English patent covering a process of making a tuagsten
filameat by means of an alloy of tungsten and nickel,
drawing this alloy into wire and then removing the nickel.
In this patent it stated the impossibility of directly making
a tungsten filament and spoke of tungsten as a non-ductile
refractory metal.

Dr. Kuzel's application covered a process of making a
filament from any one of fourteen metals, among which
tungsten was included. The process consisted of reducing
these metals to a colloidal condition which, when made into
a paste with water (no organic binder being used), was
squirted through a die to form a thread. The tungsten
particles of the thread were then sintered together to
form the filament.

It then appeared to be only a question of a proven
priority date of invention as to which of the two parties,
Just and Hanaman or Kuzel, would be granted the patent.
Evidence was introduced to the U.S. Patent Office that
Just and Hanaman had filed appHcations for their French
and British Patents on November 4, 1904. This was prior
to the U.S. application of both Kuzel (January, 4, 1906)
and Von Bolton (November 10, 1904). In July, 1911,
the Assistant Commissioner of Patents handed down a
very thorough and extended decision on the patent inter-
ference, and the patent was granted to Just and Hanaman
in February, 1912.

The Trade Mark Mazda

The trade mark Mazda was adopted by the General
Electric Company late in 1909, but is now used by more
than one manufacturer. It is not the name of a thing
but the mark of a research service rendered to the manu-
facturer by the Research Laboratories of the General
Electric Company at Schenectady, New York. It com-
prises not only the incandescent lamp research work done
by these laboratories and the data obtained from the
testing and inspection work done throughout the com-
pany, costing over a million dollars a year, but also the

100

THE INCANDESCENT LAMP

accumulation of scientific and practical data from labora-
tories, factories, etc., all over the world. The results are
transmitted to the manufacturers entitled to this service,
with such aid and information as will assist them to improve
the quality of their larrips.

A Mazda lamp is, therefore, the product of the latest
and best method of incandescent lamp making. The
filaments of all Mazda lamps are at present made of
tungsten, but when any material more suitable for the
purpose is discovered or developed, it will be used.

Persian mythology gives to their ancient god of light
the name Ahura Mazda, and to the Persians, light was
knowledge. Mazda service therefore, very fittingly stands
for the accumulation and transmission to lamp manufac-
turers of the knowledge which will enable them to produce
the best light.

The Drawn Tungsten Wire Filament

As has been stated, tungsten was known to be a very
hard, non-ductile and brittle metal which could not
be drawn into a wire. Many scientists were misled into
the belief that if it were purified it would become ductile
as Von Bolton found to be the case with tantalum. Prior
to 1906, it was the universal opinion that tungsten could
not be made ductile. It was known that when heated
to very high temperatures it could be bent, but when cool
it was always brittle.

Dr. WilHam D. Coolidge, of the Research Laboratories
of the General Electric Company at Schenectady, began
an investigation of the subject in 1906. He first produced
tungsten as pure as he could get it, and then deHberately
added various impurities to study their effect. These
experiments led him to believe that in the case of tungsten
it was not the presence of impurities which made the metal
brittle, but that the brittleness was an inherent characteris-
tic of the metal itself. His first discovery, which later gave
him the clue which he afterwards so brilliantly followed,

101

THE INCANDESCENT LAMP

consisted in finding that tungsten, carefully prepared in a
particular way, could be hammered at certain temperatures
and that by so hammering, the material could be con-
siderably elongated and its form changed. While the
metal which was thus hammered was brittle when allowed to
cool, nevertheless Dr. Coolidge had done something which
no one else had ever done and it encouraged him to continue.

At this point, he discovered a new process for getting
tungsten into a dense coherent form. This process con-
sisted in incorporating tungsten powder with a ductile
metal alloy of cadmium, bismuth and mercury, Squirting
the mixture through a suitable die and then, by heat
treatment, removing the foreign ingredients and sintering
the tungsten powder. This, so-called, amalgam process
was subsequently used in preparing thick tungsten fila-
ments from which the first tungsten wire was drawn. As the
amalgam process gave better squirted filaments, in the large
sizes, than were at the time obtainable in any other way, it
was intensively developed by Dr. Coolidge in the labora-
tories and later became the standard factory process for the
production of high wattage and series lamp filaments.

Early in 1907, Dr. Coolidge again took up the hot
working of tungsten, experimenting with a small rolling
mill such as is used by jewelers. He heated the rolls, a
most unusual operation, to a temperature of about 300
degrees Centigrade and passed amalgam process tungsten
filaments between the hot rolls, obtaining an appreciable
lengthening of the filaments. Before this time he had
discovered that he could bend amalgam process filaments
into special shapes by the application of proper but rela-
tively low temperatures, going so far as to coil the filament
into a spiral whose internal diameter was no greater than
that of a knitting needle. This in itself was a valuable
achievement, as such concentrated filaments are of value
in focusing types of lamps such as those used in automobile
headHghts.

His next work, done late in 1907 and early in 1908, con-
sisted in squeezing thick tungsten filaments between hot

102

THE INCANDESCENT LAMP

blocks of tungsten steel whose working faces had been
ground parallel and hardened. x\n appreciable extension
of the filament was obtained and when such a hot-worked
filament was broken in two and one part was heated
above the equiaxing temperature, measurements showed
that the part which had been hot-worked and not equiaxed
was stronger than the other part in the sense that it would
stand cold bending through an arc of smaller radius.

Dr. Coolidge had, then, learned that suitably prepared
amalgam process filaments could be bent, rolled and pressed
at temperatures at which hardened alloy steel tools would
not lose their temper. The hot-pressing experiments had
also shown an improvement in mechanical strength result-
ing from such hot working.

He next decided to try hot-drawing some filaments and,
guided by his earlier hot-working experience, he recognized
the need of heating the die, that portion of the filament
which was in tension, and the jaws of the pliers holding the
end of the filament. The openings in the dies naturally
were smaller than the filament, but the difference, called
"the draft," had to be very small, a fraction of a thou-
sandth of an inch, as otherwise the filament invariably
broke.

In order to introduce the filament into the opening in
the die, the entering end was pointed by a process which
he had previously invented which consisted in electrolyzing
it in a concentrated aqueous solution of potassium cyanid.
This method, unlike the ordinary electrolysis of tungsten,
reduced the diameter without rendering the surface pitted
and porous, and hence without needless weakening of the
filament at the point where it was to be grasped by the
hot pliers. The die was heated by a special gas burner;
that portion of the filament between the die and the pliers,
pulling the filament through, was heated by a hot body of
metal underneath; the pliers were heated by gas; and that
portion of the filament back of the die on the entering side
was, in some cases, heated by a gas heated metal under and
partially surrounding the filament.

103

THE INCANDESCENT LAMP

In this way, in the fall of 1908, pieces of pressed tung-
sten filament were successfully drawn through many dies,
each but little smaller than the previous one, and then it
was found that a wonderful thing had been accomplished,
the tungsten had lost its brittleness. The tungsten had
actually become bendable, and even ductile, when cold.

The Drawing of Ordinary Ductile Metals

Ordinary ductile metals, such as wrought iron, copper,
silver, gold, etc., may exist in either one of two states which
are known as the "crystalline" state and the "strain-
hardened" state. The crystalline state is the natural
condition of the metal and is that in which it exists
after it has cooled from a molten state. Under the micro-
scope, and sometimes by the naked eye, the metal will
be seen to be composed of an aggregate of crystals. Ordi-
nary workable metals are ductile in this crystalline state.
In the strain-hardened state, these crystals have been
changed into fibers, threads or plates, or in some other
way have been strained and distorted out of their original
crystalhne form.

The change from the crystalline to the strain -hardened
state is produced by mechanical working at low tempera-
tures such as by drawing the metal into wire, which is
ordinarily done at room temperature. As the crystals are
deformed by working, the metals become hard and springy
and their workability decreases. If the strain-hardened
(sometimes called "hard-drawn") fibrous metal be heated
to a certain temperature, different for each metal but always
below its melting temperature, and maintained long enough
at this temperature, the fibers break up and recrystallize.
This temperature is called the metal's "annealing" tem-
perature and with ordinary metals it restores its ductility.
Thus in drawing ordinary metals they become hard and
difficult of further working. They are then annealed,
bringing them back to their original ductile condition.

Ductility or its absence is a specific property of a metal,
not entirely dependent upon hardness or softness, strength

104

THE INCANDESCENT LAMP

or weakness, nor on any other single property. For
example, at room temperature, manganese steel is very
hard, very strong, and very ductile ; certain heat treated
steels are hard, very strong, and non-ductile; copper is
very soft, weak, and very ductile; lead is very soft, very
weak, and only sHghtly ductile; and antimony is soft,
weak, and non-ductile.

Xm^^

BRITTLE TUNGSTEN, CRYSTALLINE STATE
This photo micrograph shows the normally crystalline state of tung-
sten in which condition it is brittle.

Tungsten Ductile in Fibrous State

Under the microscope the structure of Dr. Coolidge's
ductilized tungsten filament was fibrous, while that of the
original brittle filament was crystalline. This is just the
opposite of what had been found in the ordinary ductile

105

THE INCANDESCENT LAMP

metals. He had "ductilized" a non-ductile metal and, as he
later discovered, had increased its strength enormously. Sam-
ples of drawn tungsten wire of one-thousandth of an inch in
diameter show a tensile strengthof ()()(),000 to 650,000 pounds
per sqtiare inch. The tensile strength of this drawn tung-
sten is more than thirty times that of the original sintered

DUCTILE TUNGSTEN, FIBROUS STATE
When tungsten is carefully prepared in a certain manner and worked
at certain temperatures, the crystals are deformed into fibers and
the metal becomes ductile.

tungsten, no other material showing any such increase in
strength as this. A striking feature is that no such
process as that developed by Dr. Coolidge has ever
been able to increase the ductility of any other metal, and
no mechanical process whatever had previously produced
ductility in any metal which was non-ductile.

106

THE INCANDESCENT LAMP

Dr. Coolidge also later found out that the ductile tung-
sten he had produced would, if heated to a certain high
temperature, again become brittle. This might be called its
annealing temperature, although an annealing temperature
produces ductility in ordinary metals.

Development of the Commercial Drawn Tungsten Wire
Process

While Dr. Coolidge had finally been able to make a
small piece of tungsten ductile, it required much more in-
vestigation and experiment to repeat the accomplishment
on a large enough scale to make the process commercially
practical. In fact, as will be shown, many obstacles
appeared which for some time seemed insurmountable, and
it required about two years of painstaking effort and skill
before the desired result was obtained. The difficulties and
discouragements he met with were at times almost heart
breaking.

The first piece of ductile tungsten he had produced
was made from an "ingot" (if so ponderous a name can
be used) consisting of a pressed tungsten filament 25
one-thousandths of an inch in diameter. In order to
obtain an ingot, or slug, of a reasonable size, he first tried to
press dry tungsten powder together without a binder.
He used a steel mould filled with tungsten powder and
tried to form the slug by pressure applied at the end.
This was the natural thing to do, but instead of producing
a homogeneous slug, he obtained one with a plate-like
structure.

He next tried using a mould in which the pressure was
applied at the side, but the resulting slug contained what
he called "corner cracks." These cracks caused much
difficulty and it was only after an extended study of the
effect of the amount of pressure used, the method of
applying the pressure, the design of the mould and many
experiments on various lubricating substances which
could be used on the surfaces of the mould, that he was
able to make slugs free from mechanical faults.

107

THE INCANDESCENT LAMP

The slugs finally produced were so fragile that they
could only be handled by sliding them carefully along a
smooth surface. The next step was to give them some
mechanical strength, which was accomplished by baking
them in a tube in a stream of hydrogen.

This baking was only a preliminary stage ; it was neces-
sary to heat the slugs to a very high temperature to cause
the tungsten powder to sinter together. This was done
by passing a heavy current through them, like the sintering
operation in making pressed filaments, but here new prob-
lems arose requiring the development of a special bottle.

In this heating operation the slug was mounted vertically
and at first a rigid clamp was attached to each end, the
current passing in at one clamp and out at the other.
The slug was surrounded by a metal treating bottle and
a stream of hydrogen gas passed through the bottle to
protect the tungsten from oxidizing. When the slug was
heated it shrank and usually broke in two or pulled out
at one end from one of the clamps. The bottle was full
of hydrogen and a certain amount of air was drawn in by
the first cooling resulting from the shutting off of the
current. Hydrogen and air form an explosive mixture
and the result was usually a violent explosion, the very
hot tungsten slug igniting the mixture, and the bottle being
blown to the ceiling.

To overcome the difficulty the expedient was tried of
giving the slug a slight partial treatment, reclamping it,
giving it a further slight treatment, and so on, but
dangerous explosions still occasionally occurred. The
problem was finally solved by suspending the slug by the
upper clamp, the lower clamp dipping in mercury which
was kept cool by water flowing through a copper tube.
The mercury would conduct current to the lower clamp
and allow the slug to shrink, the apparatus being so de-
signed that the shrinkage did not cause the lower clamp
to leave the mercury.

Serious difficulty arose from another cause. The slug
would occasionally break near the upper end or pull out

108

THE INCANDESCENT LAMP

of the upper clamp. The upper end of the slug in falling
would often strike the inner surface of the bottle, forming a
severe arc, and often melting a hole through the inner layer
of the bottle, which was a double walled affair, cooled by
water flowing between the walls. Such conditions were finally
overcome by using springs instead of bolts in the clamps.

Another serious difficulty remained, however. There
was a good deal of oxidization of the slug while in the
bottle, the cause of which was not clear for a long time. It
was finally found that it was due to the fact that when the
slug was at a high temperature, the convection currents in
the hydrogen gas around it were so vigorous that they
extended down to the mouth of the bottle and caused air
to be drawn in. To obviate this, the mouth of the bottle
was allowed to dip into mercury filling a circular depression
in a metal plate, which made an effective seal.

All this required several months of work, and it turned
out that all the slugs produced were entirely brittle, not
only when cold but also when hot, and so could not be
worked. This was so discouraging that it then seemed
impossible to start with a slug of anything but minute
size.

He then tried, with the help of an expert, skilled in
electric furnace practice, to produce a slug of tungsten
by heating the metal in the high temperature of an electric-
arc furnace. But this did not help, for when he attempted
to work the slug it cracked all to pieces.

Feeling that he was making so little headway on the
direct attack. Dr. Coolidge decided to drop work on tung-
sten for a time and to try hot working large masses of
molybdenum. The latter metal has some of the properties
of tungsten, but possesses some slight inherent ductility;
so he hoped that the presumably simpler problem of work-
ing molybdenum might teach him something which would
help him to work tungsten. All this effort on the hot work-
ing of the larger metal masses so far had taken over a year
of his time.

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THE INCANDESCENT LAMP

He then returned to his sintered tungsten slugs and
tried hammering them hot by hand on an anvil, but could
make no progress. Fearing that the failure was caused by
his own lack of skill, he called in two expert blacksmiths.
He found that it was possible to hammer the slug a little,
certain blows being successful, but with others the slug
would break to pieces.

He then tried his jeweler's rolling mill again, using
exceedingly small drafts, but even then the slugs cracked
badly. He found, however, that the work was being cooled
at the point where it should remain hot, so he built a
special rolling mill in which a current of about a thousand
amperes passed from one roll across the tungsten to the
other roll. This heated the slug at the point where it was
being worked, and with it he made a little headway,
but was not able to work a tungsten rod down to such a
size that it could be drawn through a die.

He then went to see a manufacturer of swaging ma-
chines. These machines have two small hammers which
operate at high speed as the machine is rotated, striking
blows on anything placed between them. The hammers
have a recess in them leaving an opening through which
the rod to be swaged is fed. The minimum size of this
recess determines the diameter of the rod after it has
passed through the machine, the hammers being usually
called swaging dies. This manufacturer had built a few
machines for hot hammering steel, but on account of
difficulties, the work was confined to short lengths of large
cross section and the machines were not adapted to hot
hammering long lengths of small cross section.

He next visited another concern where swaging ma-
chines were being used for the cold swaging of needles,
but no one seemed to think that the machines were suitable
for hot w^orking rods of small diameter. Nevertheless,
he obtained one of these machines, but when he tried it,
even with molybdenum, the metal went all to pieces in
the first two or three dies. Another difficulty was that
as the dies rotated about the work, they tended to take

110

THE INCANDESCENT LAMP

the work with them and twist it off. He tried increasing
the speed of the machine, but this only intensified the
trouble and as the material was so hard, the hammering
not only cracked the material but even the dies them-
selves.

The operating principle of the machine consisted of
striking a large number of overlapping blows to produce a
smooth surface on the material worked as it was slowly
passed through the dies. Having found that this pro-
cedure led only to failure, he decided to strike out for
himself in an opposite direction. He found that with the
ordinary swaging die each blow abstracted a certain amount
of heat from the tungsten. The next blow, struck prac-
tically in the same place, hit the spot of tungsten that had
become chilled below the most favorable temperature and
cracked it. He designed some special dies that had but a
small working face, and by feeding the rod through the
machine at fairly high speed, he was able to prevent the
blows from overlapping. This helped tremendously, and
by specially shaping the face of the dies he was finally
able to eliminate the trouble of twisting the work.

As a result he was enabled to carry a molybdentnii
(not tungsten) rod successfully through several dies
without cracking, but then another difficulty appeared.
He had been holding the heated rod in a pair of tongs,
thrusting it into the swaging machine as rapidly as possible
for half its length, and then withdrawing it. As a result,
a number of blows which overlapped each other struck the
middle of the rod, chilling it and producing cracks. To
overcome this, he provided a very powerful brake by which
he was able to stop the machine very suddenly when he
had thrust the rod in as far as he thought desirable, thus
slowing down the hammering action of the machine before
he slowed down the motion of the rod. He then with-
drew the rod, reheated it, and thrust the opposite end
in the swaging machine. Later, however, as the art
advanced as a result of his researches, it became possible
to get along without the brake.

Ill

THE INCANDESCENT LAMP

Finally, he was able by this hot swaging process to
reduce his original tungsten slugs, which were about 34
to ^ of an inch square and six inches long, to a rod having
a diameter of about J/g of ^-^ inch. However, from this
point on, his difficulties increased enormously as the size
of the rod decreased. As the rod decreased in diameter
its length of course increased, increasing the number of
blows that had to be struck, and a single blow struck under
unfavorable conditions was sufficient to crack or break the
rod. At this point the problem of bridging the interval
between f/g of an inch (or 125 mils — a mil is a thousandth
of an inch) to 30 mils seemed almost impossible with a
swaging machine. His original piece of ductile tungsten
was made from a pressed filament of 25 mils drawn down
through diamond dies, and diamond dies larger than 30
mils were not available. He tried chilled iron dies, using
swaged molybdenum, but after passing it through several
dies, it split up badly. He then tried drawing hot molyb-
denum through the dies but found it destroyed them.

His next step was to obtain a much smaller swaging
machine that could be driven at a higher rate of speed,
which permitted the work to be fed faster into the ma-
chine, the working face of the dies being still further
reduced. A small tube furnace was placed in front of the
machine and the work was fed from this directly into the
machine by a pair of rolls running at a uniform rate of speed.
As a result he was finally able to swage molybdenum, and
later tungsten, down to 30 mils.

During this whole process the workability of the
tungsten was being improved and at 30 mils it was found
to be ductile. From this point on he was then able to
draw the tungsten, which owing to its reduced size may now
be called wire, through diamond dies by methods he had
already used. This consisted of using hot dies; heating
the wire; aqua dag lubricant which, at the suggestion of
one of his assistants, was baked on the wire; small drafts;
and a gradual reduction of temperature as the work pro-
ceeded.

112

THE INCANDESCENT LAMP

While he had now been able to make a fine drawn tung-
sten wire from a relatively large tungsten slug in the
laboratory and with much patience, it did not mean that a
commercial process had been developed to manufacture
wire on a large scale. There were difficulties which had
to be met, some tungsten slugs seemed capable of being
mechanically worked, while others did not. Two lines of
research were started, mechanical and chemical, both
being carried along together.

The tungsten slugs had been heated in a gas forge. He
tried heating them in an atmosphere of hydrogen and de-
vised a special iron tube furnace for the purpose. This
helped, as it was believed that the rods took up carbon or
oxygen from the furnace gases and thereby lost much of
their workability. Another difficulty then arose. Small
shiny spots appeared on the slugs after they had been
sintered in the treating bottle. After the first swaging, the
metal in the neighborhood of these spots was found to be
brittle. Samples of this brittle metal were analyzed and
found to contain iron, which, it was decided, must have
come from the walls of the iron tube furnace. This difficulty
was overcome by placing the rods in carriers and em-
bedding them in powdered silica. A vigorous stream
of hydrogen gas was passed through the iron tube and
in this way the vapor of any iron evaporated from the
walls of the furnace was prevented from reaching the
tungsten.

But there still was a lack of uniformity in the behavior
of the various slugs. Some of them, as they came from
their first heating in the iron tube furnace, shrank more
than others when being sintered in the treating bottle,
those which had shrunk least being the more easily worked.
He thought that the ones that shrank most must have taken
up some other impurity from the furnace, so he devised an
electrically heated porcelain tube furnace. The first slugs
fired in this furnace looked much better than anything seen
up to that time. He then went on a vacation, leaving
instructions to press up, heat in the porcelain tube furnace

113

THE INCANDESCENT LAMP

and sinter in the treating bottle a hundred slugs which were
to be ready for hot working experiments on his return.

On his return he found that none of the slugs could be
worked, all breaking up in either the first or second swaging
die. This puzzled him greatly, but he finally decided, after
much investigation, that the trouble was caused by the
presence of oxygen in the sintered slugs. He was using
very fine tungsten powder which oxidizes to such an extent
that it normally absorbs a relatively considerable amount
of oxygen before it is moulded in the press. During the
first heating of the slug in the iron tube furnace, the rods
had been packed in silica and this finely divided material
had hindered the escape of water vapor resulting from the
action of hydrogen on the oxide of tungsten. The long
continued heating in this atmosphere of water vapor had
materially coarsened the tungsten powder and thus had
made it possible to remove the oxygen before sintering had
taken place. The porcelain furnace merely removed the
oxygen from the surface of the slug, and after this had
happened the surface sintered over imprisoning the balance
of the oxygen. Dr. Coolidge then made some relatively
coarse tungsten powder by melting tungsten oxide in a
crucible, crushing the resulting mass, and reducing the
oxide to tungsten. He then found that another chemist in
the laboratory had, for some other purpose, heated some
tungsten oxide in a "Battersea" crucible and also reduced
it to a coarse tungsten powder. With these coarse powders
he was able to get good results from slugs treated in the
porcelain furnace, provided they were kept out of contact
with the porcelain tube. Otherwise they would take up
the glaze from the tube, which caused a net work of fine
cracks to develop on the surface of the rods after they had
been partially worked.

The problem of producing tungsten wire in quantity
had now been solved, but lamp filaments made from this
early wire "offset" badly when burned on alternating
current. This was a difficulty which had also been found
in the tantalum lamp. It was discovered, however, that

114

THE INCANDESCENT LAMP

wire made from the coarse tungsten powder produced
from the oxide heated in the Battersea crucible did not
offset. Dr. Coolidge reached the conclusion that the

DR. COOLIDGE AND MR. EDISOX, 1922
Dr. Coolidge showed Mr. Edison, when he visited the Research Lab-
oratory in Schenectady in 1922, the swaging machine which he
had developed and with which he was able to make tungsten
ductile on a commercial scale.

tungsten had absorbed certain substances from the Batter-
sea crucible which had some effect on the offsetting.
After much experiment he found it possible to prevent
offsetting by directly mixing the tungsten powder with
small amounts of certain other substances.

115

THE INCANDESCENT LAMP

The Temperature of the Working

The temperature at which tungsten is worked is an
important part of Dr. Coolidge's invention. With other
metals, except in the special case of molybdenum, working
below the annealing temperature will always reduce duc-
tility. The reverse is true with tungsten; its ductility is
created by working it below its annealing temperature.

Whenever any of the other metals has been worked hot,
above its annealing temperature, it has been because it was
easier and cheaper to give it the desired form at that
temperature, or it was desired to secure the superior
mechanical properties associated with the "fine grained,"
structure, or, by working it at or above its annealing
temperature, it was possible to work and anneal at the same
time thus avoiding a special annealing process.

The actual annealing temperature of tungsten becomes
lower the greater the amount it is worked below its anneal-
ing temperature. Tungsten can be worked above its
annealing temperature, but its ductility is destroyed and it
will revert to its crystalline state, becoming brittle when
cool. The working range is from about 1650 degrees C,
a high white heat, down to about 350 degrees C, which is
below a dull red heat; the more the metal is worked, the
lower the working temperature. The initial working
operations must be carried on at high temperature, other-
wise the tungsten would break in pieces on account of its
brittleness at low temperature. The high temperature also
reduces its hardness.

The fact that heating to temperatures above the
annealing temperature destroys the effect of previous
working was utilized in a curious and interesting way.
After it had been discovered how to make an ingot of
tungsten that could be swaged and worked down to small
diameters, there was found a tendency for the tungsten to
split longitudinally at some stage of the process, usually
before the wire had been brought down to the desired size.
It split up into a bundle of fibers almost Hke the fibers of a
hemp rope. A certain amount of working the tungsten is

116

THE INCANDESCENT LAMP

good, but too much working spoils it, so the object was
to subject it to that certain amount of working and then
stop. As various sizes of wire are necessary for the various
wattages and voltages of lamps, the exact amount oi
working was accomplished by the simple expedient of
reducing the standard size ingot to one of a particular size
under conditions which would not change its internal
structure to any considerable extent, and then properly
work it down to the size of wire desired.

1

^^.-^tS^^^-^

i

DRAWN TUNGSTEN WIRE LAMP, 1911
Dr. Coolidge's invention of drawn tungsten wire materially simpli-
fied the manufacture of the tungsten filament lamp and greatly-
increased its ruggedness.

Announcement and Adoptioji of Drawn Tungsten Wire

Dr. Coolidge's success in being able to make ductile
tungsten was announced in March, 1910. In 1914, he was
awarded the Rumford Medal by the American Academy
of Arts and Sciences for his scientific triumph. This is
perhaps the highest recognition of the sort to which an
American scientist can aspire, the medal being granted
for the most important discovery or useful improvement
in heat or light. A patent was granted to Dr. Coolidge
in December, 1913.

117

THE INCANDESCENT LAMP

The making of tungsten filaments was changed over
to the drawn wire process, beginning with the latter part of
1910. In the early part of 1911, the drawn wire lamps
were put on the market. Over half a million dollars'
worth of the pressed filament apparatus had to be scrapped,
as well as nearly another half million dollars' value of
unsold pressed filament lamps.

Drawn tungsten wire filaments are very strong, and
consequently the lamp is very sturdy, a marked improve-
ment over the fragile pressed filament lamp. The lamp is,
therefore, much more practicable and the breakage in ship-
ment is reduced. The enormous increase in the strength of
the filament greatly increased the use of the lamp under
such severe conditions as those met within its application
to automobiles, street railway and steam railroad cars, etc.
Drawn wire filaments are much cheaper to make than
pressed filaments, so that it became possible to materially
reduce the price of the lamps. Drawn wire can be readily
coiled, which greatly simplified the manufacture of con-
centrated filament lamps for focusing purposes.

Ductile tungsten can be drawn to such an exact diameter
and cut to the desired length so accurately that practically
all lamps made are of the voltage and efficiency for which
they are designed. In fact the variation in voltage is so
small that these lamps are not photometered, as all previous
kinds of lamps had to be, to determine their voltage.
Sample lamps are constantly tested for voltage and effi-
ciency, and these tests show that lamps as made today vary
less in voltage and efficiency than previous lamps, even
after the latter had been tested and sorted for voltage.
Thus the necessity for a multipHcity of voltages because of
the variations in lamps was eliminated, all lamps could, if
desired, be made for a single voltage. As it seemed im-
practical for all plants to readjust their voltage to one
standard, three standard voltages, 110, 115 and 120 volts,
have been adopted. At present more than 90 per cent of
the standard lighting lamps are of these three voltages,
and the stock necessary to properly supply the demand has
been greatly simplified.

118

THE INCANDESCENT LAMP

In the usual sizes of lamps the filament is of such a small
diameter, a few thousandths of an inch, that it is impossible
to determine the diameter accurately by a micrometer.
It is accurately measured, however, by weighing a definite
length, a few inches of the wire, in a sensitive torsion
balance, which will determine its weight and hence, by
calculation from its specific gravity, its diameter, to within
three millionths of an inch.

OFFSET TUNGSTEN FILAMENT
After a filament has been lighted for the first time it has a crystalline
structure. If the faces of the crystals fall in one plane across the
diameter of the filament, offsetting may occur.

m

THORIA PREVENTS OFFSETTING

This high magnification photomicrograph shows the thoria globules

which tend to key the crystals together, preventing offsetting.

Non-Sag Drawn Tungsten Wire

When a lamp is first lighted, the long fibrous grains of
the drawn wire, heated above their annealing temperature,
are changed to the equiaxed grains of an annealed metal.
These grains, during this transition, absorb each other,
gradually increasing in size until further growth is retarded
or stopped. The cessation of growth of the grains may
be attributed to several causes, not the least of which is the
presence of impurities in the metal.

119

THE INCANDESCENT LAMP

The crystals composing the wire are, to the best of
present knowledge, held together by amorphous tungsten.
This material acts as a binder to hold them together
and in place, but, at very high temperatures, it is not as
rigid as the crystals themselves, consequently the positions
of the latter may become altered.

Should the faces of one or more crystals fall in one plane
across the diameter of the filament, offsetting will occur,
that is, sections of the filament will slide sidewise and
it will soon burn out due to the decrease in cross-
section at this point. Fairly small crystals with minute

"^ ;^^

Sag Wire

Non-Sag Wire

CRYSTAL GROWTH IN TUNGSTEN FILAMENTS
By removing nearly all the slight amount of impurities in a tungsten
filament, the crystals become long and overlap and so make a sag-
resisting wire which does not oflFset. The sag resisting feature is of
great advantage in coiled filament lamps.

particles of thoria, which is hard at the high temperature,
will retard offsetting, the thoria particles tending to key
the crystals together.

The thoriated wire, however, bends easily at this high
temperature due to the fact that the proportion of amor-
phous material present is greater than that in a large
grained wire. Thus, if the crystals could be allowed to grow
to a large size, there would be relatively less of the amor-
phous tungsten present and, if these crystals overlapped

120

THE INCANDESCENT LAMP

and interlocked with each other, a wire should be produced
which would remain stiff and would not readily sag nor
offset at high temperature.

Dr. Aladar Pacz, of the General Electric Company, made
a study of this. He reasoned that if it were possible to get
rid of the minute impurities and eliminate the use of
thoria, a wire of large overlapping crystals might be
obtained which would neither sag nor offset. It might be
possible to get rid of these impurities by purposely inserting
certain substances. These substances should not vaporize at
the relatively low temperatures at w^hich the moulded tungs-
ten slug is given its preliminary heating in hydrogen gas, but
should readily vaporize at the relatively high temperature at
which the slug is sintered in the treating bottle by a heavy
electric current. Thus the substances, coming out of the
slug as it is being sintered, might carry with them the
minute impurities it was desirable to get rid of.

Dr. Pacz tried mixing various substances with the
tungsten powder, and after many experiments finally evolved
a process, by which tungsten is produced in apparently
such a pure state that the wire filament, made by Dr.
Coolidge's process, when lighted for the first time, imme-
diately crystallizes in such large over-lapping crystals
that it does not materially sag or offset. The
crystals are many hundred times larger than those of
thoriated wire.

In a Mazda C (gas-filled) lamp it is most important
that the coiled wire should not sag materially. If it does,
part of the helix opens up, allowing the gas to more readily
circulate between the turns of the helix and thus cool the
wire to a greater extent. This lowers the temperature of
the filament, reducing its candle power and efficiency.
Certain turns of the helix tend to sag together, and if the
turns touch each other they short circuit themselves.
Dr. Pacz's invention was, therefore, of great value in the
Mazda C lamp, so that it not only considerably improved
the maintenance of candle power of the lamp during its life
but also increased its average efficiency throughout life.

121

THE INCANDESCENT LAMP

Non-sag wire is used only in coiled filament lamps. In
the straight filaments used in some vacuum lamps, the
bends of the filament around the anchors operate at a
much lower temperature due to the conduction of heat
away from the filament at these places. As a consequence
the filament does not sag at the bends.

122

CHAPTER FOUR

The Vacuum, ''Getters", and The Gas-
Filled Lamp

THE VACUUM

The vacuum was one of the elements of Edison's original
lamp and still is in the majority of lamps made today.
In the early days of lamp manufacture all lamps
were exhausted on Sprengel mercury pumps, which con-
sisted of a glass "fall" tube down which mercury was
allowed to fall. The fall tube was connected at the top to
a branch tube, one end of which was connected to the lamp
to be exhausted, the other end being connected to the
upper reservoir of mercury. The mercury trapped bubbles
of air from the lamp and its weight forced the bubbles down
and out of the end of the fall tube, which dipped into the
lower reservoir of mercury. The mercury from the lower
reservoir was pumped back to the upper by an Archimedes
screw pump.

A very high degree of vacuum is necessary in a vacuum
lamp, but, since it is impossible to produce an absolute
vacuum, the degree of vacuum is measured by the pressure
of the residual gases in the bulb. Atmospheric pressure at
sea level is about fifteen pounds per square inch which is
equal to the weight of a column of mercury about 760 milli-
meters high. The degree of vacuum is measured in microns, a
micron being one-thousandth of a millimeter, and in modern
lamps the degree of vacuum is often less than one micron
mercury pressure, or about a millionth of that of the
atmosphere at sea level.

In June, 1881, it took five hours to exhaust a lamp, each
operator taking care of about fifty pumps, with one lamp

123

THE INCANDESCENT LAMP

on each pump. The chief difficulty was then and still is
getting the moisture, in the form of water vapor, out of the
lamp bulb. This moisture adheres to the surface of the glass
and the glass must be heated to liberate it. No matter how
hot the bulb is heated, more moisture will be liberated if
the bulb is heated still hotter, so the bulbs must be heated

SPREXGEL VACUUM PUMPS
Mercury, dropping down the "fall" tube, trapped bubbles of air and
so exhausted a lamp. This originally required five hours. In-
provements reduced the time to thirty minutes.

during exhaustion, or just before it, hotter than they will ever
become in use. In practice they are heated to about 300° C.
After the moisture is Hberated it must be removed from
the bulb. The mercury pumps would not draw it out, so
from the beginning it was absorbed by phosphoric anh}^-

124

THE INCANDESCENT LAMP

dride which was held in a small glass cup attached to the
pump. In the early days this phosphorus cup was not close
enough to the lamp and the absorption of moisture had to
take place through five or six inches of glass tubing. This
was one reason for the long time required to exhaust lamps
in 1881. Later this condition was improved, the dryer
being put as close as possible to the lamp, about 23/^ incfies,
and this shortened the time of exhaust a great deal.

The vacuum pump itself was much improved, larger
tubing being used so that the pump required three times
as much mercury to operate it. The contraction which
limited the flow of mercury to the pump was changed from
glass to iron. Glass contractions got dirty and gradually
reduced the flow of mercury, but iron did not get dirty and
kept the pumps working at full capacity. All these changes
ultimately reduced the time required to exhaust a lamp to
thirty minutes.

The copper plated filament connections and carbon paste
connections liberated a good deal of gas when heated.
Before the vacuum became good there came a stage in
which it was conductive. In this condition, when the fila-
ment w^as burned at high temperature, this cross current,
passing through the partial vacuum and creating a blue glow
in the bulb, heated the filament connections red hot and
drove the gas out. The carbon filaments themselves gave
out very little gas when heated.

The condition of the vacuum in the Sprengel mercury
pumps was indicated by the size of the bubbles of gas
passing down the fall tube of the pump. As the vacuum
improved these bubbles got smaller and smaller until they
could not be seen. This condition was known as a solid
tube, the tube being filled with mercury with no bubbles
showdng in it. This was the indication of a good vacuum
and the lamp was then sealed off. A solid tube indicated
a vacuum of one thousandth of an inch (about forty
microns) of mercury pressure or less. These mercury pumps
were used from the beginning until 1896, when the Malignani
chemical exhaust process was introduced.

125

THE INCANDESCENT LAMP

Malignani Chemical Exhaust

Arturo Malignani was a home made engineering genius.
He lived in the town of Udine, in the northern part of Italy,
right at the foot of the Austrian Alps, where he built an
electric lighting plant for the town and made his own electric
lamps. He did not have mercury pumps and his mechanical
pump would not make a good enough vacuum, about one
millimeter (1000 microns) mercury pressure being the best
he could get. He made the great discovery that, when he
had this poor vacuum in a lamp, if he liberated phosphorus

MALIGNANI CHEMICAL EXHAUST, 1896
This chemical method of improving a relatively poor vacuum, quickly
obtained by a piston vacuum pump, to the high degree required
in a lamp, reduced the time of exhaust from half an hour to less than
two minutes.

vapor in the lamp while the filament was burning at high
incandescence and the bulb was full of blue glow, the glow
suddenly disappeared and a high vacuum was produced.

Malignani painted the inside of the exhaust tube of the
lamp with red phosphorus. Then, when the filament was
raised to high incandescence and the bulb was full of blue
glow, he closed the connection between the pump and the

126

THE INCANDESCENT LAMP

lamp and heated the exhaust tube enough to vaporize the
phosphorus. This drove the vapor inside the lamp, the
blue glow disappeared and a good vacuum resulted.

This invention revolutionized the art of lamp exhaus-
tion. The General Electric Company bought Malignani's
U. S. patent, and adopted this method of exhausting
lamps. It enabled one operator with one pump to exhaust
a lamp a minute with more uniform result than could be
produced by the old method which required thirty
minutes.

THE "GETTERS"

Before the expiration of the Edison lamp patent in 1894,
the Waring Electric Lamp Company marketed lamps called
"Novak Lamps" which, instead of having a high vacuum,
had a small amount of bromine vapor in the bulbs, usually
about 13>2 millimeters (1500 microns) mercury pressure.
This bromine very materially reduced the discoloration,
and that which did occur was greenish and not black. It is
believed that the carbon molecules thrown off from the
incandescent filament combined with the bromine vapor
to form the greenish compound on the bulb. The bromine
was gradually used up and, after a few hundred hours
burning, the lamp had good vacuum. This bromine was
what is now called a "getter" and this was the first, though
unrealized, use of a getter.

When the Edison patent expired, the manufacture of
this lamp was abandoned in favor of the high vacuum lamp.
The Novak lamp was invented by John Waring, who super-
vised its manufacture. He was a man of unusual character
and promise, and his death, which was due to an explosion
in his laboratory, was deeply regretted by all who knew him.

The word "getter" is now applied to any active agent
used inside the bulb, either to assist in getting a vacuum,
or to improve the quality of the lamp, usually by pre-
venting the blackening of the bulb.

The use of phosphorus to improve the vacuum, in-
vented by Malignani, has already been described. The

127

THE INCANDESCENT LAMP

phosphorus was never called "getter" in connection with
Malignani's chemical exhaust.

In 1908 or 1909, John T. Marshall invented the present-
day method of exhausting tungsten filament lamps without
lighting the filament. He coated the filament and mount by
dipping the mounts in a mixture of phosphorus and water.
After the lamps were sealed off, the filament was burned at
high incandescence; a blue glow appeared, and a good
vacuum resulted.

Phosphorus is now used as a getter to assist in getting
the vacuum in all vacuum lamps, it being applied to the
filament as a coating. After sealing off the lamp, this coat-
ing of getter is vaporized by flashing the filament to a bright
incandescence. At this time, a blue glow appears in the
bulb for about a second. Disappearance of the blue glow
is always associated with "clean-up," or reduction in pres-
sure. The explanation of the formation of blue glow is
somewhat as follows : Under the influence of the voltage
applied across the filament, electrons emitted from the
negative end of the filament are accelerated with appre-
ciable velocity toward the positive end. If there are pres-
ent sufficient residual gas molecules, a large number of
collisions occur between electrons and gas molecules with
the consequence that the molecules are ionized; that is,
they are dissociated into an electron and a positively charged
residue (positive ion). These separated parts naturally tend
to recombine, and during the process of recombination,
radiation is emitted, which is perceived as blue glow.

The action of phosphorus in getting the vacuum, or in
" cleaning-up " the lamp as it is called, is not perfectly
understood, but it is believed to act in two ways. The
phosphorus vapor combines chemically with oxygen and
water vapor, and the products of these combinations are
carried to the bulb and held there. It is also believed that
the phosphorus, which has condensed on the bulb under the
conditions which exist when the filament is at intensive
incandescence and blue glow is in the lamp, adsorbs other
gases with which it does not combine chemically, and holds

128

THE INCANDESCENT LAMP

them on the bulb. These gases may be subsequently
liberated in their original condition if the lamp bulb is
heated hot enough to vaporize the phosphorus.

Many experiments have been tried to determine the
nature of the action of these getters, and some evidence,
although it is not conclusive, has been obtained. The
residual gases in vacuum lamps, after sealing off, are, on the
average, about 25 microns. In gettered lamps, this
pressure will be reduced to less than one micron
when the lamp has burned for a few seconds,
provided the applied voltage is high enough. In
lamps below forty volts, the reaction is much
slower, and may be of a different nature. There
is evidence that the reaction of the getter with the
residual gas is not predominantly chemical, since such
getters as phosphorus, siHca, aluminum or manganous
oxide will, when applied to the filament as a getter, clean
up such gases as hydrogen, nitrogen, carbon monoxide,
carbon dioxide, oxygen, water vapor, and to a lesser degree,
argon, at about the same rate, and to about the same
residual pressure, regardless of which getter or gas is used.
Chemical action probably takes place between phosphorus
and oxygen, and also water vapor. In addition to any
action which may take place in the vapor phase, probably
the most important reaction takes place on the bulb wall.
When the lamps with phosphorus, silica, aluminum or
manganous oxide getter are burned, the getter having been
thrown to the bulb wall and the gas having been cleaned up,
a second clean-up can be obtained by admitting a small
quantity of gas and again flashing the lamp. Only a Hmited
quantity of gas can be made to disappear on a single coating
of getter in this manner. It is beHeved that phosphorus
has a continuing action during the life of the lamp in case
any water vapor is liberated in its interior.

The general conclusion is that the vacuum clean-up
must be largely an adsorption, by the getter on the bulb
wall, of gases activated in some manner by an electrical

129

THE INCANDESCENT LAMP

discharge of sufficiently high voltage. It is believed that
the action of the phosphorus getter is solely to get and
keep the vacuum, as it acts on gases only.

There is another kind of getter used in all tungsten
filament vacuum lamps, the action of which is not to get
or maintain the vacuum, but is to reduce the blackening of
the lamp. This getter is usually a fluoride, and is now
applied to the filament as a coating. In practice, it is
mixed with phosphorus, and the mixture is put on the
filament.

When the lamp is flashed after exhaustion the getter
vaporizes and condenses on the bulb, where it remains.
During the life of the lamp, molecules of tungsten fly from
the hot filament to the bulb and slowly blacken the bulb,
but the coating of getter reduces this blackening very much.

The reaction to prevent blackening by fluoride is showni
to take place on the bulb wall by placing a small piece
of glass, about the size of a dime, on the inside of the lamp,
and letting it protect one small spot on the bulb from a
deposit of getter while the lamp is being flashed. The small
piece of glass is then removed to some other location and
the lamp burned for several hours. The spot where the
glass rested when the lamp was flashed will blacken much
more rapidly than the remainder of the bulb due to the
absence of getter at that point. This black spot has sharply
defined edges, and has the same shape and size as the
protecting glass. One explanation of prevention blackening
is due to some optical experiments at the Philips Lamp
factories at Eindhoven, Holland. The result of these
experiments indicate that the particles of vaporized tung-
sten are held in a sort of colloidal suspension in the getter,
and in this condition will not absorb so much light as if
allowed to agglutinate and form a continuous layer. Some
engineers think that this is due, in part at least, to chemical
action.

A third class of getters was formerly used to a consider-
able extent, but is little used now. These getters were
placed in a cavity in the glass filament support, where the

130

THE INCANDESCENT LAMP

heat caused them to give off a continuing supply of gas.
Different materials have been used, some of which give off
gases, such as oxygen, or a halogen gas, which combine
with the vaporized' tungsten to form a Hght colored deposit
on the bulb. Barium chlorate is an example of an oxygen
getter. This is used today in vacuum series lamps, which is
the only use today of a getter of this class.

A little oxygen has a beneficial getter action in either
carbon, tantalum or tungsten lamps. In all these lamps,
oxidized copper supports which slowly liberated oxygen,
gave better results than supports made of non-oxidized
metal.

Other getters of this third class ^deld gases which are
halogen compounds, and which have a regenerative action,
combining with the vaporized tungsten, carrying it back
and depositing it on the filament. Tungsten oxychloride
is a regenerative getter. Potassium thallium chloride is
another. The latter was used commercially for a long time
on some lamps. When the temperature condition of the
getter was right, the lamps remained clear and did not
change in resistance or candle power. But temperature
conditions varied so much that the lamps gave variable
results, and the getters are no longer used.

Getters are also used in gas-filled lamps. Phosphorus
is used in gas-filled lamps, being applied to the filament
as in vacuum lamps, and, when vaporized, combining
with the water vapor and oxygen in the lamp, thus
purifying the gas with which the lamp is filled. Carbon
and carbon compounds are also used as getters in gas-
filled lamps. They are applied to the filaments in the same
manner as a phosphorus getter. Both getters take care of
water vapor and oxygen — the phosphorus possibly has a
continuing action during the life of the lamp. The action
of the carbon, however, will cease when all of the carbon
has been removed from the filament.

Barium ozoamid is used by one European lamp manu-
facturer in gas-filled lamps. It prevents blackening by the
liberation of nascent nitrogen which is very active in com-

131

THE INCANDESCENT LAMP

bining with vaporized tungsten and water vapor. This
getter is decomposed by heat when, after the lamp has
been exhausted, it is flashed high in the gas.
Skaupys Getter

Franz Skaup^^ an Austrian chemist, invented the use of
getters in metal filament lamps to lessen the blackening
of the bulb caused by the deposit of the filament material

TUNGSTEN LAMP WITH SKAUPY'S "GETTER," 1912
The chemicals called ''getters," in the hollow end of the glass rod
supporting the filament, vaporized as the lamp burned, reducing
the blackening of the bulb.

on the bulb. Skaupy's idea was to use chemicals in the
lamp which would convert this black deposit into one of a
lighter shade, so that less light would be cut off from the fila-
ment during the life of the lamp. The chemicals as used by
Skaupy did not improve the vacuum; on the contrary a
gas was purposely formed in the bulb as the lamps burned
This was opposite to what lamp engineers considered
desirable, as the belief was that nothing should be done to

132

THE INCANDESCENT LAMPS

impair the vacuum. Skaupy's invention is, therefore all
the more meritorious. He applied for a U. S. patent
which was granted in November, 1915.

In Skaupy's getter certain chemical compounds of the
halogen group of elements (fluorine, bromine, iodine,
chlorine) are put inside the bulb and remain there after
the manufacture of the lamp has been completed. These
compounds will break up when heated, releasing some of
the atoms of the halogen element used, the rate of release
depending on the temperature and pressure.

For example, withthallic chloride (which was commer-
cially used) chlorine gas is evolved which will combine with
tungsten, forming tungsten chloride, which is lighter in
color than tungsten itself. If the chlorine gas is evolved
at the proper rate by heating the thallic chloride to the
proper temperature, it will combine with the tungsten which
evaporates from the filament as the lamp burns, without
attacking the tungsten filament itself. If it evolved too
slowly, the deposit will contain black tungsten, as an
insufficient quantity of chlorine gas is evolved to combine
with all of the tungsten which vaporizes. If evolved too
fast, the tungsten filament itself will be attacked, thereby
shortening the life of the lamp. It is, therefore, important
that the thallic chloride getter be kept at a given tempera-
ture as the lamp bums.

This was accomplished by inserting the getter in a cavity
in the end of the glass arbor supporting the filament
anchors, the upper end of the arbor being made of glass
tubing. The getter was held in place by glass wool, and the
end of the tube constricted to prevent the getter and wool
from dropping out.

In acttial practice a double halogen compound was used,
potassium thallic chloride, a chemical combination of two
salts, potassium chloride and thallic chloride. ThalHc
chloride readily absorbs water vapor and was apt to do so
before it was put in the lamp. Water vapor is very detrimental
in a lamp, as it causes the lamp to blacken rapidly. The
double chloride compound does not easily absorb water vapor.

133

THE INCANDESCENT LAMP

The use of getters was particularly desirable in the larger
sizes of lamps, since such lamps blacken to a greater extent
during their life than those of the lower wattages. This is
because the relation of bulb surface to filament surface
becomes smaller in the higher wattage lamps, causing a
denser deposit on the bulb. Skaupy's getter was, therefore,
used on the 100-watt and larger sizes of 110- volt types of
lamps. It was also found that his getter was so active that
it was impractical to use it in lower wattage lamps, as it
could not be prevented from attacking the filament.

It is an expensive manufacturing proposition to make
a hollow arbor to hold the getter. This method and its
location was found to be the only practical one with this
getter in order that it should reach the proper temperature.
Many investigations were made to see if other chemical
compounds could be used with simpler manufacturing con-
struction, or to permit taking advantage of similar chemical
reactions in lower wattage lamps.

Dr. Fink's Potassium Iodide Getter

Dr. Colin G. Fink invented a getter which was used in
1912 in the smaller sizes of lamps, namely those of 15 to 40
watts for 110-volt circuits. It consisted of potassium iodide
mixed with water, a drop of which was put on the end of
the glass arbor holding the filament, after which the drop
was dried by baking the mounted filament in an oven
before the mount was sealed in the bulb.

Potassium iodide is not as active as thallic chloride,
but was commercially suitable for the lower wattage lamps,
although it was impractical for use on 60-watt and larger
lamps. During the life of the lamp, the iodide is decom-
posed by the heat from the filament, iodine vapor being
released which combines with the vaporizing tungsten,
forming a light colored deposit in the bulb.

Needhams Getter

Harry H. Needham, of the General Electric Company,
invented a getter which was more active than Dr. Fink's,
but less so than Skaupy's, and wassuitable for 25- to 60-watt.

134

THE INCANDESCENT LAMP

110-volt lamps in which it was used. A patent was appHed
for in October, 1912, and granted in June, 1916, covering
the method of appHcation and use of double halogen salts,
such as cryolite, which is a combination of sodium and
aluminum fluoride, and which was commercially used.

The double salt was mixed with a binder, such as water
glass, a drop of which was put on the anchors supporting
the filament, care being exercised that the getter did not

TUNGSTEN LAMP WITH NEEDHAM'S GETTER, 1912
This method of application greatly simplified the lamp construction.
The chemicals used made the getter practicable in smaller sizes
of lamps.

touch the filament, as otherwise it would cause the filament
to fail at the point of contact. The getter was then dried
by baking the filament mounts in an oven before they were
put in the bulb. During the life of the lamp, the heat

135

THE INCANDESCENT LAMP

from the filament decomposed the cryolite releasing fluor-
ine gas, which combined with the vaporizing tungsten,
forming a light colored deposit.

Red phosphorus was mixed with this getter, the lamp
being exhausted and sealed off without lighting the filament.
After the base had been put on, the lamp was slowly
lighted for the first time by gradually increasing the voltage
applied to it. This is called "flashing," and by this means
the red phosphorus in the getter became heated and
vaporized, improving the vactium in accordance with
Malignani's scheme as previously described.
Friedericli s Oxygen Getter

Ernst Friederich, a German, invented a getter consisting
of an oxygen compound, barium chlorate being commer-
cially used. He applied in June, 1913, for a patent in this
country, which was granted in September, 1917. The
barium chlorate was later mixed with manganese dioxide
which acted as a catalyzer; that is, it assisted in breaking up
the barium chlorate so that it would give up oxygen gas
when heated. Red phosphorus was also mixed with this
getter as in Needham's scheme, but the getter was located
in the hollow end of the glass arbor supporting the filament
anchors as in Skaupy's construction. It was used in lamps of
150 watts and above and is now used in vacuum series lamps.

The oxygen gas, released by the heat of the filament,
which decomposed the barium chlorate, combined with the
vaporizing tungsten, forming a light colored deposit.
GilVs Invisible Getter

Frederic W. Gill, ofthe General Electric Company, applied
for a patent in June, 1915, which was granted in November,
1918, covering a getter which could be applied directly
to the filament. The first getter commercially used, super-
seding Needham's getter, was ordinary table salt (sodium
chloride) dissolved in water and sprayed on the mount.
Red phosphorus was included in the getter as in Needham's
scheme. When the lamp was lighted for the first time, the
sodium chloride immediately vaporized from the filament
and condensed on the walls of the bulb in an invisible layer.

136

THE INCANDESCENT LAMP

Care had to be exercised not to spray the mount too
much, as too great an amount of the solution would cause
the bulb to become iridescent. This led to the development
of another method now used, also covered by patent, of
putting the getter on the filament in such a way that the
amount put on could be more accurately controlled.

A fluid mixture consisting of either sodium iron fluoride
or cryolite (sodium aluminum fluoride) is made with red
phosphorus and gun cotton, the latter dissolved in alcohol,
ether and amyl -acetate. The drawn tungsten wire, before
it is put on the anchors, is run through this paste, which
forms a coating on the wire. The coated wire is then run
through a plain solution of gun cotton to give it a further
protective coating which dries and hardens on the wire.

THE GAS-FILLED LAMP

Dr. Irving Langmuir joined the staft' of the Research
Laboratories of the General Electric Company at Schenec-
tady in 1909, while they were in the midst of Dr. Coolidge's
invention of ductile tungsten and its application to incan-
descent lamps. One of the troubles, as has been explained,
was the curious phenomenon of "offsetting," a tendency
for the filament to divide into little sections of short length
which sHd sidewise over each other. Dr. Langmuir under-
took a stud}^ of this phenomenon, which led him to a study
of the gas given off by a tungsten filament at very high
temperatures.

The necessit}^ of a high degree of vacuum appeared to
be of even greater importance in a tungsten than in a carbon
filam nt lamp. The candle power given out by a lamp dur-
ing its life decreases as it bums, the decrease being mainly
due to blackening of the bulb caused by material leaving the
filament, depositing on the inner surface of the bulb, and thus
shutting off the light emitted by the filament. It was believed
that the blackening of the bulb might be caused by slight
traces of gases in the bulb, the rapid motion of the gas
molecules striking the surface of the filament causing its

137

THE INCANDESCENT LAMP

disintegration. Some engineers thought that the disintegra-
tion might be due to chemical or electrical action of the
gases and others thought it might be due to true evaporation.

Study of the Residual Gases in a Vacuum Lamp

It appeared, therefore, that a study of these traces of
gases in the bulb was desirable, as their elimination
might improve the lamp. Attempts to improve the lamp
by obtaining a better vacuum than usual had not been
very successful, and while it appeared that in operating a
filament at its normal temperature, the vacuum gradually
improved to a point better than that directly obtainable by
any known method of exhaust, there were clear indications
that undue blackening was caused by imperfect exhaust.
The faint traces of residual gases were in such minute
quantities that their pressure was less than that possible
of measurement with the most sensitive vacuum gauge.
The failure to improve the lamp by a new method of ex-
haust might mean that the vacuum had not been improved,
since the pressures were too low to measure.

The residual gases in the bulb, after it has been ex-
hausted to about one micron or less, were found to consist
of water vapor, oil (hydrocarbon) vapors, carbon monoxide,
carbon dioxide and hydrogen. By operating a filament
above its normal temperature, more gases come out, and
it was found that these gases not only came from the fila-
ment but the heat caused gases to come out of the anchors,
leading-in wires and the glass as well. The actual gases
from the filament were found to be small in quantity, as
later work showed that the apparently inexhaustible sup-
ply of gas from within the filament was produced by
its decomposing the water and hydro-carbon vapors
present at extremely low pressures in the bulb. The
actual gases from within the filament were mainly carbon
monoxide and small amounts of hydrogen and carbon
dioxide. The gases from the anchors and leading-in
wires were also small in quantity. If the bulbs were
externally heated so as to obtain higher temperatures than

138

THE INCANDESCENT LAMP

that received from the filament, large quantities of gases
were driven out from the glass. These gases were mainly
water vapor, a small amount of carbon dioxide and a still
smaller amount of nitrogen.

The determination of these gases was a great achieve-
ment, as it was necessary for Dr. Langmuir to devise special
apparatus to make qualitative and quantitative analyses
for the determination of five different gases from but one
cubic millimeter of total volume. Heretofore, it had been
impossible to make determinations when such small quan-
tities were involved.

Small quantities of various gases, up to about a tenth
of a millimeter pressure, were then put into lamps to study
their effect. Hydrogen was found to dissociate, that is,
the molecules of hydrogen broke up into their two atoms,
in which condition the gas is chemically very active. Dry
hydrogen did not have the slightest tendenc}^ to blacken
the bulb. Oxygen combined with the hot filament, forming
an oxide which coated the bulb with an invisible layer, but
it did not cause blackening. Nitrogen did not attack the
filament, but it combined with the tungsten which evap-
orated from the filament, changing the deposit from black
to brown. Carbon monoxide behaved almost exactly like
nitrogen and thus could not be responsible for blackening.
Carbon dioxide attacks the filament, producing an oxide of
tungsten, the carbon dioxide reducing to the monoxide, but
without blackening the bulb.

Water vapor, even at very low pressures, was found to
produce blackening. This was surprising, as neither of its
constituents, hydrogen and oxygen, acting alone, produces
blackening. The explanation seems to be that the water
vapor, coming in contact with the hot filament, is decom-
posed, the oxygen combining with the tungsten which de-
posits on the bulb. The chemically active atomic hydrogen
formed attacks the tungsten oxide deposit, and reduces it to
metallic tungsten, forming water vapor again. This cycle
may be repeated indefinitely, so that a small quantity of
water vapor will quickly blacken the bulb.

139

THE INCANDESCENT LAMP

The effects of many other gases and vapors were studied,
among which were chlorine, bromine, iodine, sulphur,
phosphorus, phosphine, hydrochloric acid, methane, argon,
etc., but in no case did these gases produce blackening,
provided great care was taken to have them extremely
dry. The behavior of argon was interesting. At pressures
above five microns and below one micron, a glow occurs
in the bulb, current flowing from one filament leg to the
other through the gas. This so-called *' Edison effect "caused
the bulb to blacken rapidly. The small amount of argon
which might exist in an ordinary lamp could not, however,
produce such blackening.

This study led Dr. Langmuir to the conclusion that if
the blackening of the bulbs of ordinary lamps was caused
by imperfect vacuum, it must be due to water vapor.
He devised new methods of producing extremely high
vacua, improving the vacuum from a millionth to much
less than a billionth of an atmosphere. Extra precautions
were taken to remove all traces of water vapor and, to make
sure that water vapor was not evolved by the bulb becoming
hot, lamps were even run with the bulbs completely im-
mersed in liquid air during their entire life.

The unexpected result of his work was that with all
these precautions, the lamps were not materially better
than the best lamps regularly made in the factory. There
seemed to be no hope of improving the lamp by getting a
better vacuum, the vacuum in the ordinary lamp being
good enough. The investigations did show however, that,
excepting water vapor, the presence of gas in small quan-
tities in tungsten filament lamps did not seem to cause
blackening and that the only one of the suggested causes of
blackening which had not been investigated was the true
evaporation of the filament. This he probably never would
have discovered if he had not endeavored to find an explan-
ation for the various phenomena found, rather than by
trying to look for a definite object.

To test out the theory that true evaporation is the cause
of blackening, Dr. Langmuir made many experiments to

140

THE INCANDESCENT LAMP

determine the rate of loss of weight of tungsten filaments
operated at various temperatures. The actual results
agreed remarkably well with the theoretical figures, which
indicated that blackening of well-made tungsten filament
lamps is caused by true evaporation of the filament.

Introduction of Gases at Atmospheric Pressure

It was possible that the presence of a chemically inert
gas inside the bulb would reduce the rate of evaporation
of the filament provided the phenomenon was simply one
of evaporation. This is somewhat similar to the effect air
pressure has on the boiling point of water. At sea level,
water boils at 212 deg. P.; at high altitudes where the air
pressure is less, the boiling temperature is less. Thus if a
gas pressure were put in the lamp it might retard the
evaporation of the filament, though it had usually been
found that the presence of a considerable amount of gas
caused an increase in the rate of disintegration of a heated
metal. Dr. Langmuir had shown that low pressures of
gases, except water vapor and argon, did not produce
blackening of the bulb, and, therefore did not produce
disintegration in the ordinary sense, and that hydrogen,
nitrogen, argon and mercury vapor seemed chemically
inert towards tungsten at high temperatures.

To test this out, a tungsten filament lamp was made which
was filled with carefully dried and purified hydrogen at at-
mospheric pressure. The filament was run at the same tem-
perature as that of vacuum lamps operating at one watt
per candle. The loss of heat, due to its conduction away
from the filament by the gas, was so great that 17 watts
were required for each candle power (less than 0.6 lumens
per watt) actually produced in this lamp. The heat is
conducted away from the filament by its contact with the
gas, on the same principle that causes the handle of a poker
to become hot when the other end is put into a fire.
Furthermore, the heated gas rises, circulating in the bulb
and forming convection currents, thereby rapidly transfer-
ring the heat to the upper part of the bulb. This is why

141

THE INCANDESCENT LAMP

so much more electrical energy (watts) had to be put into
the filament to maintain it at the same temperature as
that obtainable in vacuum, where these heat losses do not
occur.

This hydrogen filled lamp burned for more than 360
hours without showing any blackening of the bulb, but the
loss of heat was so great, and so much more electrical energy
was required to maintain the proper temperature, that it
was impractical from a commercial standpoint. Sub-
sequently it was found that while the heat conductivity of
hydrogen is high compared with other gases, the amount
of electrical energy required to operate the lamp was
abnormally great, because at high temperatures the
hydrogen molecules break up into their two atoms (as Dr.
Langmuir had previously discovered), absorbing an added
amount of electrical energy.

Experiments were then tried with tungsten filaments in
mercury vapor at atmospheric pressure and the heat loss
by convection was found to be extremely small in com-
parison with hydrogen, so small that the filament could be
operated for about a minute at 21 J^ lumens per watt. The
experiments showed that the presence of mercury vapor very
greatly retarded the rate of evaporation of the filament.

Nitrogen at atmospheric pressure was next tried and
found to be entirely inert towards the high temperature
tungsten filament. Comparatively so little heat was taken
away from a large diameter filament operating close to its
melting temperature that it could be operated for a moment
at 22 lumens per watt. At the melting temperature of
tungsten, it would theoretically give an efficiency of about
25 lumens per watt in vacuum. The rate of evaporation of
tungsten at high temperature in nitrogen was also found to
be less than in vacuum.

A slight increase in the temperature of a filament, which
requires but a small increase in electrical energy (watts)
will make a great increase in the amount of light it
gives. This, however, is done at a sacrifice to the life
of the lamp. The rate of evaporation of the filament at a

142

THE INCANDESCENT LAMP

given temperature having been found to be less in gas than
in vacuum, the next thing to be determined was whether
or not the filament could be operated in gas at a higher
temperature (and so obtain more light for the same life)
than possible in vacuum and yet not require more watts
for the actual candle power obtained. In other words,
was it possible that a gas-filled lamp, having the handi-
cap of large heat losses by convection, could be made
more efficient than a vacuum lamp not having this handicap,
both lamps having the same life. A careful study was
therefore undertaken of the laws of heat convection from
filaments at high temperatures in various gases, since the
knowledge on this subject was extremely meager.
Study of the Dissipation of Heat from Hot Wires

Dr. Langmuir had studied abroad in 1903-5 and had
made some researches on the effect of highly heated plat-
inum wires in dissociating steam, and other vapors and gases.
He had become interested in the laws governing the dissi-
pation of heat from hot wires, and when he returned to
this country he continued this investigation, but had little
opportunity to experment until he entered the Research
Laboratories of the General Electric Company. Some
experiments he conducted at Pittsfield, in 1911 on electric
heating devices broadened his knowledge.

Further experiments were then made to determine the
laws of heat convection, by operating platmum wires in
air, carbon dioxide, and hydrogen, and tungsten wires
in hydrogen, nitrogen, mercury vapor and argon. He
found that the heat loss varies with the temperature,
according to a simple function of the heat conductivity of
the gas, and also varies with the diameter of the wire
according to a rather complicated formula. From this he
derived an equation by which he could calculate the heat
losses from a wire at any given temperature in various gases.
This showed that the heat lost by convection increases
(around high temperatures) rather slowly with increases
in temperature in the case of nitrogen and mercury vapor,
but increases very rapidl}^ in the case of hydrogen. It also

143

THE INCANDESCENT LAMP

showed that the heat loss from very small wires, such as
those of about a thousandth of an inch in diameter, was not
very different from wires of several times this diameter.
This was most unexpected; one would think that if the
size and, therefore, surface of the wire were doubled, the
rate at which heat was lost would be doubled, but this is
not true.

Dr. Langmuir's explanation of this is that a wire or
filament, in the case of a lamp, seems to hold a layer of hot
gas, about a sixth of an inch in thickness, which adheres to
it, the thickness of this gas film being independent (within
certain limits) of the diameter of the filament. Halving
the diameter of the filament, therefore, does not halve
the thickness of the filament with its gas film. For ex-
ample, a filament two-sixths of an inch in diameter would,
with its gas film, have a diameter of four-sixths of an inch.
A filament of one-sixth of an inch in diameter, 50 per cent
less than that of the former, has a diameter of three-sixths
of an inch with its gas film which is 25 per cent less than
that of the former (four-sixths as compared with three-
sixths). Hence the effective cooling surface of a thin fila-
ment is relatively greater than that of a thick filament. From
this it will be seen that with small wires more heat is pro-
portionally lost than with large wires.

The increase in temperature necessary, due to the pres-
ence of gas in the bulb at about atmospheric pressure, in
order that a gas-filled lamp could operate at the same effi-
ciency as a vacuum lamp, would, therefore, be very much
greater with thin filaments than with thick ones. Thus in
nitrogen, Dr. Langmuir estimated that a filament of 1.1
thousandths of an inch in diameter (the size of tungsten
filament of a 25-watt, 110-volt vacuum lamp) would have to
operate at about 2600 deg. C. to give nine lumens per watt,
the present efficiency of the 25-watt vacuum lamp. The
25-watt vacuum lamp now operates at about 2050 deg.
giving a life of a thousand hours, and if operated at 2600
deg. would last about half an hour. It will be seen, therefore,
that the reduction in rate of evaporation (and consequent

144

THE INCANDESCENT LAMP

increase in life) due to the gas would have to be very great
to overcome the handicap imposed by the gas in lamps
having small diameter filaments.

On the other hand, a filament of 13 thousandths of an
inch in diameter, which would be the size of the filament in a
1000-watt, 110-volt vacuum lamp, if such a lamp were made,
would only have to operate in nitrogen at 2300 deg. as
compared with 2200 deg. C.in vacuum for the same efficiency.
A 1000-watt, vacuum lamp operated at 2200 deg. would give
a thousand hours life and if operated at 2300 deg. would last
about sixty hours. Thus with thick filament lamps the
handicap of the gas should not be so great.

These calculations did not prove that the introduction
of gas would produce a better lamp, but indicated that if
it were possible at all, it could be done more easily by using
large diameter filaments. There was nothing to indicate how
great the reduction in evaporation would be, so that it
would have to be found by experiment, but the calculations
showed in what manner the experiments should be con-
ducted.

Experimental Gas-filled Tungsten Filament Lamps

Dr. Langmuir made two sets of thick filament
lamps, one set operating in nitrogen at atmospheric pres-
sure and the other set in vacuum. In both sets the fila-
ments were operated at the same efficiency in order that
the life results could be compared. The nitrogen-filled
lamps were failures.

This was very discouraging and probably to the ordinary
experimenter would have ended the investigation. But
Dr. Langmuir had built up a theory that the nitrogen-
filled lamps should be better, his former experiments show-
ing that the evaporation of the filaments in gas was less
than in vacuum, although its extent had not been
determined. It seemed as if the extent should be great
enough to overcome the handicap of the extra heat losses
due to the gas, provided thick filaments were used. This
faith encouraged him to continue his research, but before

145

THE INCANDESCENT LAMP

trying the experiments again he carefully examined the
lamps he had tested to see if he could find any clue that
might show him the cause of their failure.

He noticed that the deposit of evaporated material
from the filament was located at the upper part of the bulb
where it was expected to be, having been carried there by

GAS-FILLED TUNGSTEN FILAMENT LAMP. 1913
This lamp, invented by Dr. Irving Langmuir, was twice as efficient in
the larger sizes as the vacuum lamp. The bulb was filled with
nitrogen gas at about atmospheric pressure. The filament was
coiled.

the circulating currents of gas in the bulb, but the deposit
was black instead of brown. He had found in previous
experiments with nitrogen that the othenvise black deposit
of tungsten was changed to brown, owing to the formation
of tungsten nitride. It seemed strange that this had not

146

THE INCANDESCENT LAMP

happened in these lamps, so he concluded that there must
have been some trace of water vapor in the nitrogen gas
which was responsible, in spite of the extraordinary precau-
tions he had taken to prevent its presence.

He then repeated the experiments, taking still greater
precautions to eliminate any water vapor, and this time his
experiments were successful. The filaments he used were
relatively very large, two to four hundredths of an inch in
diameter, requiring from 20 to 60 amperes of current. Such
lamps for 110-volt circuits would consume from about 2000
to 6000 watts, and would be very large compared with the
ordinary vacuum tungsten filament lamps of 25, 40 and 50
watts used in the home, and large even when compared
with the biggest vacuum lamp then made for commercial
lighting, which consumed 500 watts.

Dr. Langmuir then conceived the idea that the effect of
a large filament might be obtained by properly coiUng a
small one. In designing such coiled filaments, it was evi-
dently desirable to wind the filament on as large a mandrel
as possible to obtain the advantage of the large diameter.
It was also desirable to have the coils as close together as
possible. Tungsten is a relatively soft material at the
operating temperatures of these lamps. If too large a
mandrel were used, the weight of the filament would pull
out the helix very materially in a few hours, so that the heat
lost by convection would be increased. This sagging of the
wire might also allow the lower turns of the coil to touch
each other and short circuit, so the spacing between turns of
the coil must not be too small. Careful experiment showed
that certain mandrel sizes and spacings gave the best
results. He then was able to make a gas-filled lamp, taking
a little less than ten amperes, and consuming 1000 watts
on 110-volt circuits, which was twice as efficient as a vacuum
lamp for the same life. Further experience made it possible
to produce a 750-watt lamp and these lamps were put on the
market late in 1913. Dr. Langmuir applied for a patent in
April, 1913, which was granted in the same month
of 1916.

147

THE INCANDESCENT LAMP

In order to distinguish the vacuum from the gas-filled
lamp, the former is called a Mazda B lamp and the latter
a Mazda C lamp. If these designating letters after
the trade mark Mazda had been desirable at the time
the pressed filament lamp was being commercially made,
the pressed filament lamp would have been known as a
Mazda A lamp.

dr. LAXGMUIR and MR. EDISOX, 1922
When Mr. Edison visited the Research Laboratories at Schenectady
in 1922, Dr. Langmuir showed him a 30,000-watt lamp he had
made for experimental purposes. This is the largest lamp ever
made, giving 100.000 candle power.

Exhaustion of Gas-filled Lamps

The moisture exhaustion problem is present in the gas
filled lamp to as great, if not to a greater, degree than in the

148

THE INCANDESCENT LAMP

vacuum lamp. It is just as necessary to get rid of this mois-
ture in the gas-filled lamp and it is more difficult because
the blue glow of ionization which is such a great help in
clearing up the moisture with phosphorus in the vacuum
lamp does not appear in the gas-filled lamp. Other m.eans,
which are not so simple and easy as the clean up with phos-
phorus, must be used to get rid of the moisture. Washing
out the moisture with dry gas is the most practical and is
now used in regular factory practice. Several washings are
necessary; dry air can be used for the first washings and
dry nitrogen for the later ones.

High vacuum pumps are not necessary in exhausting
gas-filled lamps because the washing out removes all the air
and other gases and vapors without requinng a high vacuum
at any time. The pumps used in this work have large
capacity and produce a vacuum of about two-tenths of an
inch (about 800 microns). When these lamps are sealed
off they contain a sufficient amount of argon (with about 15
per cent of nitrogen) to make the pressure inside the lamp
equal to atmospheric pressure when the lamp is burning.

Although phosphorus does not clean up the moisture
in a gas-filled lamp as it does in a vacuum lamp, it has a
good effect in taking care of the moisture which is left
after the lamp is sealed off. It is put on the filament in
gas-filled lamps as in vacuum lamps. Carbon and carbon
compounds are also used, these and phosphorus possibly
having a continuing action during the life of the lamps in
taking care of water vapor and oxygen. The action of
carbon, however, will cease when all of the carbon has been
removed from the filament.
Previous Attempts to Make Gas-filled Lamps

Mention has been made that several Russian scientists
had attempted fifty years ago to make lamps having a
graphite burner operating in nitrogen gas. In 1878-9,
Sawyer had tried the same thing, as has been stated, and
failed. Even Edison had tried the use of nitrogen in the
experimental lamps he made in the early eighties, after he
had invented his practical vacuum lamp, and he also failed.

149

THE INCANDESCENT LAMP

Edison knew that nitrogen would cool the filament, and
tried to compensate for this by using a filament of smaller
cross-section. He did not know why he failed, but found
out that his gas-filled lamp lasted only one twentieth as long
as a vacuum lamp at the same efficiency. Even after Dr.
Langmuir's success, the Research Laboratory of the
General Electric Company was unable to produce a gas-
filled carbon lamp as good as a vacuum carbon lamp.

The "Novak" lamp, previously mentioned, which was
made for a while in 1892, and which contained bromine gas
at a pressure of about two one-thousandth parts of the
atmosphere, cannot be construed as a gas-filled lamp. The
Courts decided it was a vacuum lamp and therefore infringed
upon Edison's basic vacuum lamp patent. Gettered lamps
as originally made, in which a slight trace of gas was gen-
erated as the lamps burned, cannot be said to be gas-filled
lamps either as the vacuum in such gettered lamps is at
least one-thousandth part of atmospheric pressure, whereas
the gas in the lamp invented by Dr. Langmuir is at abovit
atmospheric pressure.

In this connection Dr. Langmuir found that there was
no material advantage in having the gas pressure in the
bulb much greater than that of the atmosphere. Even if it
were desirable, there might be danger of the lamp's
exploding. The gas is put in the bulb at slightly less than
atmospheric pressure, so that when the lamp is lighted and
becomes heated, the gas expands to a pressure about equal
to that of the atmosphere.

Commercial Developments of the Gas-filled Lamp

The first commercial lamps, those of 1000 and 750 watts
for 110-volt circuits, were made with round bulbs. The
circulating currents of gas in the bulb in rising made the base
quite hot, the heat being conducted to the socket holding
the lamp. In order to lower the temperature of the base
and socket, the bulb shape was changed by putting a
tubular glass neck on the upper part of the bulb, a mica disk
keeping the gas from circulating m the neck. The simpler

150

THE INCANDESCENT LAjMP

shaped straight sided bulb was adopted soon after, which
later was changed to pear shape.

As the art of making Mazda C lamps progressed, it
became possible to make smaller sizes. In July, 1924, 500-
and 400-watt lamps for 110-volt circuits were developed,
these lamps, on account of their smaller diameter filaments,
not being quite as efficient as the larger sizes. They were,
however, considerably more efficient than the same size of
Mazda B lamps, which then disappeared from the market.

MAZDA C lamp, JANUARY, 1914
A glass neck was put on the bulb, a mica disk preventing the circu-
lating hot gas from reaching the base.

Series Mazda C lamps were also made which displaced
the vacuum lamps formerh^ used. These (as well as the
former vacuum lamps) were more efficient with the 6.6-
ampere filament in the ordinary sizes used, so the 6.6-am-
pere circuit for street lighting became the standard.

151

THE INCANDESCENT LAMP

Lamps for 220-volt circuits were developed but, of
course, could not be made in as small a size as those for
110 volts, as the 220-volt filament is smaller in diameter
than that for 110 volts for a given wattage. Concentrated
filament lamps for projection service were also developed
for such uses as floodhghting, motion picture projection,
etc.

MAZDA C LAMP, JULY. 1914

Straight sided bulb used, a mica disk deflecting the circulating hot gas

away from the base.

Theefficiency of the Mazda C lamp is so high and the
simplicity and convenience of the incandescent lamp is so
great, that the carbon arc lamp was gradually displaced and
has now practically disappeared from use. The only other
forms of electric illuminants now in use are the magnetite

152

THE INCANDESCENT LAMP

arc lamp used in street lighting, and the Cooper-Hewitt
mercury vapor arc, often used in photography. The
magnetite arc gives a brilliantly luminous white light.
The mercury arc is valuable in photography on account of
the high actinic value of its light, to which the photographic
negative is particularly sensitive.

MAZDA C LAMP, 1915
Pear shaped bulb about as now used.

Stih lower wattage Mazda C lamps for 110-volt cir-
cuits were developed, the 200- and 300-watt lamps being
put on the market in October, 1914. Argon gas with a
small amount of nitrogen was and is now used on account
of its lower heat conductivity, with consequently less cool-
ing of the filament. The lamps are therefore more efficient

153

THE INCANDESCENT LAMP

and it is possible to produce lower wattage Mazda C
lamps which are more efficient than Mazda B lamps of
this wattage and voltage. While Dr. Langmuir had found
that pure argon in a lamp is a conductor of electricity, so
that current would arc across from one end of the filament
to the other, the lamp thus short circuiting, it was also
found that such conditions were eliminated by adding
about fifteen per cent of nitrogen gas to the argon. Argon
is one of the constituents of the air, but is present only in
small quantities, about one-half of one per cent. The
necessity for developing a process to obtain argon in reason-
able quantities caused some time to elapse before the gas
became available in sufficient amounts to make an argon-
filled lamp commercial. This gas has made it practicable to
make lamps consuming a current as low as half an ampere.
On 110-volt circuits the 50-watt lamp is therefore available,
the minimum wattage, of course, decreasing as the voltage
decreases. Thus on 60-volt circuits, 25-watt lamps can be
had; 15 watts on 30 volts; etc. This limit of half an
ampere does not quite apply on very low voltages, as in
such cases the filament is much shorter, and therefore
the amount of heat conducted away by the leading-in
wires becomes proportionally greater, so that the minimum
size increases with very low voltage lamps.

On 6-S-volt automobile lighting circuits the 21 candle-
power Mazda C headlight lamp is now standard, it being
a legal requirement to use this lamp in certain states.
The lamp consumes about 23/2 amperes.

It is uneconomical to use Mazda C lamps of smaller
sizes than those given above, because, while it is possible to
make them, their efficiency would be no better than that of
a vacuum lamp for the same life. They can be made to give
a higher efficiency, but their life would be correspondingly
shortened. As the art progresses it may be possible some
day to make still smaller Mazda C lamps which would be
more efficient than the same wattage size of Mazda B
lamps and yet have the same life.

154

CHAPTER FIVE
Leading-in Wire Developments

The electric current which heats the filament inside the
bulb to incandescence is carried to the filament by two
wires which pass through the glass chamber. These wires
must make an air-tight joint with the glass in order to
preserve the vacuum and, in a gas-filled lamp, to prevent
either the air entering or the gas leaving the bulb.

In the beginning, platinum was the only material known
which would answer the purpose and it was used for many
years. It was comparatively cheap in the early days, about
six dollars an ounce, but the cost gradually increased. As
the cost increased the amount used was reduced.

Substitutes for platinum have been sought almost from
the beginnmg, and some lamp manufacturers quite early
used nickel-steel wire with fair success. This nickel-steel
alloy can be made to have the same expansion as glass,
but it does not stick to the glass and is never one hundred
per cent efficient. The seal between the leading-in wires and
the glass is made at high temperature when the glass is soft
and, as it cools down, the wire and glass must stick to-
gether as they contract to the lower temperature. This is a
greater range in temperature than that between the lighted
and unlighted lamp, m which the wire and glass must also
stick together to make an air tight seal.

The leading-in wires present other problems beside
making a tight joint with the glass. They must be good
conductors of electricity, which nickel-steel is not. So in
many lamps, copper wires were and are now welded to the
wire imbedded in the glass. At the present time pieces of
copper wire are, in all lamps, welded to these short wires
imbedded in the glass, passing outward to connect with the
terminals of the base to which they are soldered. In vacuum
lamps, copper wires are used going inward to connect with

155

THE INCANDESCENT LAMP

the filament, it having been found that copper is the best
material for filament connection. It is always oxidized
in making the lamp, because the oxide acts as a beneficial
"getter" in vacuum lamps. In gas-filled lamps, nickel
wire is much better than copper for filament connections.
Copper oxide has a bad effect, while clean nickel is the best
material known for the purpose.

Original!}^ the seal between the leading-in wires and the
glass was made by fusing a piece of small glass tubing
around each wire, two such wires with their glass "petti-

ORKUXAL STEM SEAL, 1880
This shows how current was passed
through the glass bulb to the fila-
ment inside, in the first lamps
commercially used in 1880.

FLAT STEM SEAL, 1881

This greatly simplified the glass work

of the stem. This construction

has been used ever since.

coats " being inserted in a stem tube. The end of the stem
tube which went inside the bulb was closed by fusing it
around the glass petticoats on the wires. In the latter part
of 1880 the glass work of the stem seal was greatly simplified.
The petticoats of glass were omitted, the end of the stem
tube being flattened together about the two wires. This
method has been used ever since.

Clamps

The connections between the leading-in wires and the
filament have been a problem from the beginning. At first
a little screw clamp was used which held the enlarged end
of the carbon filament in its jaws, the other end of the clamp
being fastened to the platinum leading-in wire. At first
these clamps were made of platinum and later of nickel.

156

THE INCANDESCENT LAMP

These screw clamps were used until early in 1881, when
the copperplated connection came into use. In this arrange-
ment a piece of copper wire was welded to the platinum
wire, the latter being sealed in the glass. The other end of
the copper wire was flattened quite thin, bent double, folded
about the enlarged end of the filament and the connection
made good by copperplating. As long as this connection

/

I

EDISON LAMP, 1889

The length of the seal was reduced so that less platinum was necessary
for the leading-in wires.

was used the filaments were made with enlarged ends so
that the part of the filament which was in contact wath
the copper would not become hot enough to melt the
copper or vaporize it.

In 1886, carbon paste joints were introduced. At first
the carbon paste was made of india ink and fine graphite,
but soon a better paste was made of two kinds of graphite,
one of which contained a considerable amount of clay.
This graphite mixture was mixed with a binder composed
of a solution of sugar and gum arable. These paste joints
were baked in an oven to about 400 deg. F. to partly car-

157

THE INCANDESCENT LAMP

bonize the binder, othenvise in damp weather some of the
joints would absorb moisture and become loose before
they were sealed in the bulb.

For large sized filaments a special paste was used, con-
sisting of coarse graphite, soft coal and coal tar pitch with
sugar and gum arabic binder. After these joints had
been baked, each was painted with a little red phos-
phorus and was heated red hot on a fine gas jet. The
heating decomposed the hydrocarbons, drove out a lot

EDISOX LAMP, 1890
The amount of platinum wire in the seal was further reduced by im-
bedding the welds between the copper and platinum wires in the
seal.

of gas and smoke, and left a hard piece of coke for the joint
which gave out very little gas during exhaustion.

At the present time a material called "aquadag" is
used for the paste joint in the few carbon lamps made.
Aquadag is an extremely fine graphite powder mixed with
water. When dry it becomes pure carbon and yields prac-
tically no gas in exhaustion. This enables the exhaustion of
the present carbon filament lamps without lighting up, for
most of the gas which appeared in the previous carbon fil-
ament lamps during exhaustion came from the paste joints.

158

THE INCANDESCENT LAMP

When the pressed tungsten filament came into use, the
connections between the filament and the leading-in wires
were made by fusing the two together with an electric arc.
This was done in a reducing gas atmosphere to prevent
burning the filament. This practice was continued as
long as pressed filaments were used.

At first the connections for drawn wire filaments were
made by forming short tubes in the ends of the leading-in
wires, inserting the ends of the filaments in the tubes and
flattening and crimping the tubes on the filament ends.
This made a good connection, but the construction was
expensive. It was simplified by what is called the hook
connection. The end of the leading-in wire was flattened
and folded over on itself, forming a hook. The end of the
filament was placed inside the hook and the hook pressed
hard on the filament, which imbedded the hard filament wire
in the softer leading-in wire. This also made a very good
connection and is in general use today. Some large size
filaments are electric spot welded, and the very largest sizes
are electric arc welded, to the leading-in wires.
Substitutes for Platinum Leading-in Wires

The first substitute wire commercially used on a large
scale was that invented by Byron E. Eldred, which is
covered by a patent applied "for in October, 1911, and
granted in December, 1913. This wire consisted of a
nickel-iron alloy core which was dipped in an acid copper-
sulphate bath to give it a slight coating of copper, then
silver plated and further covered by a platinum sheath.
This composite wire was so proportioned in its parts
that it was designed to have a slightly lesser coefficient
of expansion than glass, so that in cooling down from
the high temperature at which the seal is made to the
temperature at which this part of the lamp operates, a
pinch effect of the glass on the wire was obtained. It was
commercially used from 1911 until the early part of 1913.

The use of the non-oxidizable platinum outer sheath
was deemed necessary, as glass would not "wet," that is,
make a hermetic seal with, or stick to, a bare wire of any

159

THE INCANDESCENT LAMP

base metal or of nickel-iron or other alloy if the wire were
made large enough to be used as a leading-in wire. The
intermediate copper and silver was for the purpose of
making a tight union between the nickel-iron core and out-
side platinum sheath w^hich could not be directly made.

Dr. Colin G. Fink, of the Research Laboratories of the
General Electric Company, invented an improved wire
which was put into commercial use in 1913, superseding
Eldred's wire. Fink's wire consisted simply of a nickel-iron

ASSEMBLY OF MATERIALS OF DUMET WIRE.
This leading-in wire, which took the place of platinum in 1913, consists
of a nickel iron core with a copper sheath. After brazing the
two together and drawing to the proper diameter, the wire is
coated with borax.

core, dipped in acid copper-sulphate to give it the thin cop-
per coating, and inserted in a brass sheath in order that
the outer copper sheath could be readily brazed to the
nickel-iron core. This wire has an expansion coefficient
that was practically the same as that of glass. The sheath
is about 20 per cent by volume of the wire, the proportions
of the core being about 45 per cent nickel and 55 per cent
iron. This wire is even better than platinum itself and

160

THE INCANDESCENT LAMP

its use has resulted in a much smaller percentage of leaky
lamps. While copper oxidizes readily, it was found that if
the pinched seal is heated somewhat longer than formerly,
the glass absorbs the oxide and makes a very tight union.
This wire is called "dumet" wire. Dr. Fink applied for a
patent in June, 1912, which was granted in June, 1924.

The sealing in of dumet wire was improved by W. L.
Van Keuren, of the General Electric Company, by coating
the wire with borax. Van Keuren applied for a patent on

COATING DUMET WIRE WITH BORAX

this in December, 1913, which was granted in June, 1918.
The dumet wire is heated to slightly oxidize it, and is then
dipped in a solution of borax which in dr\dng and heating
forms a copper borate w4th the oxide and makes a ready
seal with the glass. Under the conditions which exist in
sealing the wire in the very hot glass, the copper borate is
largely absorbed in the glass and the union between

161

THE INCANDESCENT LAMP

wire and glass becomes very tight. The wire makes a
tighter joint with glass than platinum, and is a better
material for the purpose. It is also relatively inexpensive
to make compared with platinum, which has risen steadily
in cost and is now well over one hundred dollars an ounce.

About twenty years ago, Geist invented a leading-in
wire composed entirely of copper. He used a copper wire
about sixteen thousandths of an inch in diameter and
flattened it at the point at which it was sealed in the
glass, so that it was very thin. He also made a round hole
in the center of this flat part. For some reason he could
not make these seals consistently effective, but he did
succeed with a large majority of them. Recently this
invention has been further developed and when the
flattened parts are made much thinner, about one and one-
half thousandths of an inch, cross section, the wires make
perfect seals. An automatic machine has been developed
and many thousands of trial lamps have been manufac-
tured using all copper leading-in wires of this type. The
copper unites so firmly with the glass that even though it
shrinks more than glass, the shrinkage of these very thin
parts does not pull them away from the glass. No hole is
now made in the thin section of copper.

In cases where the requirements to be met by the lamps
necessitate the use of a specially hard glass in the seal,
which will stand high temperatures without softening, large
tungsten wires are used for the leading-in wires. Since the
temperature expansion coefficient of such hard glass is
about the same as that of tungsten, the combination of the
two results in a tig^ht seal.

162

CHAPTER SIX
Glass Construction

When Edison began experimenting on electric lamps
he, like all other experimenters, made the glass chamber
in two parts which were separably fitted together. This en-
abled him to renew a filament easily. Later when he realized
that he must use a thin high resistance filament, he also re-
alized that the very high vacuum, which was necessary to
preserve this thin filament, could not be maintained in a two-
piece glass envelope, as the joint was often subject to leaks.
He then made a very bold decision. He abandoned the two
separable piece construction and with it the abihty to
replace a broken filament. He fused the two parts of the
bulb inseparably together, sa^dng, "I will make the lamps
so long lived and so cheap that they can be thrown away
when the filament burns out."

This one-piece glass chamber was one of the elements
of the combination which he patented and which the courts
decided covered all successful incandescent lamps. This
glass chamber consists of two principal parts: the bulb,
and the inside part, or stem, which carries the leading-in
wires and filament.

Bulb Making

At first the bulbs were made by hand from one -inch
tubing. Shortly after the lamp factory was started, bulbs
were made at the Corning Glass Works, being hand made
and free blown from glass taken directh^ from the furnaces.
These free blown bulbs were used by the Edison Lamp
Works for about twelve years, although other lamp manu-
facturers adopted moulded bulbs much earlier. The hand
made moulded bulbs were uniform in size and shape, while
the free blown bulbs varied a great deal and had to be
gauged and sized into groups of similar dimensions.

163

THE INCANDESCENT LAMP

The hand made moulded bulbs were used for about
twenty-five years before machines were developed to
make them. Bulbs are now made by a ponderous auto-
matic machine which takes the molten glass from the

BULB BLOWIXG MACHINE,
This ponderous machine turns out 50,000 bulbs per working day of 24
hours and greatly reduces their cost.

furnace in measured amounts, shapes it, blows it in a mould
and delivers the moulded glass bulb to another machine
which removes the superfluous glass from the neck of
the bulb. The completed bulbs are then automatically
delivered to a conveyor which carries them through an
annealing furnace to the inspectors where they are handled
for the first time. Each machine has twenty-four arms on

164

THE INCANDESCENT LAMP

which the bulbs are made, the machine making 70,000
bulbs per working day of 24 hours.

Automobile headlight bulbs and bulbs for most minia-
ture lamps are made from tubing in automatic machines
which blow them in moulds. A very few bulbs for special
types of miniature lamps are still made by hand from tubing
held in a horizontal lathe.
Stem Making

The inside part or stem is now and always has been
made from tubing. Stems have passed through several

EARLY HAND BLOWN STEM. 1881

An enlargement was blown on a piece of glass tubing to which the neck
of the bulb was sealed.

FLARED STEM. 1893

This was much simpler to make, less glass was used and the seal with
the bulb was less liable to crack.

changes of form and methods of manufacture. In the very
early stems, an enlargement was blown at about the center
of a piece of tubing, the enlargement serving as a foundation
to which the neck of the bulb was fused. The tubing was
left long enough to be used as a holder while the stem was
being sealed to the neck of the bulb. After this seaHng-in
operation, the extra length of tubing was cut off and thrown
away. Later the enlargement on the stemtubing was omitted,
the stem consisting of a straight piece of tubing with thelead-
ing-in wires sealed in one end. The tubing was still made long
enough to hold the stem while it was being sealed in the
bulb, the extra length then being cut off and thrown away.

165

THE INCANDESCENT LAMP

In 1893, the short stem with the flared end, which had
been developed in the Thomson-Houston factory, was
adopted. No glass was cut off and wasted in this stem
and it made a seal which was less liable to crack than the
older forms.

With this stem, as with all previous stems, the neck
of the bulb was cut off the desired length and the stem
sealed to the rim on the end of the neck of the bulb. Later
this was changed, the long neck of the bulb was not cut
off, the flared stem was inserted well inside the neck and the
excess neck cut off by the sealing-in fires at the exact point
where the flare joined the bulb. This was a great improve-
ment. The seals had less glass in them and so were less
Hable to crack, and did not have to be annealed as was the
case with the previous ones. The long bulb neck also kept
the water vapor, formed by the combustion of the gas, from
getting inside the bulb and so made the exhaustion of the
lamps easier.
Stem Making Machines

All stems were made by hand until 1901, when J. W.
Howell, aided by W. R. Burrows, made a successful stem
making machine which is essentially the same as the present
day machine. It was a four-head vertical machine which
enabled unskilled labor to make two or three times as many
stems per day as a skilled operator could by hand.

The flared stem tube was inserted in the heads, the
two leading-in wires placed inside the tube, and the anchor
wire (of the carbon lamp) put in a holder which held it in
position so that its end was inside the tube. These
were heated in three positions while the work rotated, the
hot end of the tube being squeezed into a flat mass, in the
third position.
Flaring the Stem Tube

A number of different machines have been made for
flaring the end of the stem tube. At first the pieces of
glass tubing were placed in chucks by hand, the chucks
rotating the tubing in the gas fires and the flare being

166

THE INCANDESCENT LAMP

formed by a hand tool. Later entirely automatic machines
were made which placed the tubes in the chucks, formed
the flares and delivered the flared tubes to the stem making
machines.

STEM MAKING MACHINE, 1901

Stems were made by hand until this machine was developed by J. W.
Howell, aided by W. R. Burrows. It enabled unskilled labor to
make more than twice as many stems as skilled labor could pre-
viously produce by hand.

Other automatic machines have been developed which
make the flares on the ends of long tubes, the gas fires
cutting off the desired length of flared stem tube. This

167

THE INCANDESCENT LAMP

method is considered the best because the tubing is cut
by the fires while it is soft, whereby cracked and irregular
edges are eliminated.

Tubulatmg

The first glass working tool was the "bulb punch,"
developed by William Holzer, of the Edison Lamp Works,

TUBULATING MACHINE, 1903
This machine was developed by W. R. Burrows. On the left, a hole
was blown in the bulb by air pressure while the glass was softened
by a gas flame. On the right, the exhaust tube was welded to the
hole in the bulb.

early in LS83. This tool punched a tit in the round end
of the bulb, the glass at this point being softened by
a gas flame. The protruding glass of the tit was

168

THE INCANDESCENT LAMP

afterward cut off, leaving a hole where the exhaust
tube was later sealed on to the bulb.

About 1903, William R. Burrows developed a tubulating
machine. A fine pointed gas flame was allowed to play
on the rounded end of the bulb, a shght air pressure being

SEALIXG-IN MACHINE, 1896
This was developed by J. W. Howell and was the first of the modern
machines. It is essentially the same as those now used and enabled
the production per operator to be doubled.

put in the bulb. As the glass became softened, the air
pressure blew a hole through the softened glass, blowing
the flame away from the glass and so making the hole
of uniform size. The exhaust tube was then welded to
this hole. This machine remained in use about twenty

169

THE IXCANDEvSCEXT LA:\IP

years, or as long as bulbs were tubulated on the round end,
and until the invention of the Mitchell and White method
of tubulating the stem seal, which is described later.

Sealing-in Machines

The first glass working machine was a sealing-in
machine, called the "Dufunny" and made by Edison about
18S9, to seal the stem in the bulb. This was a single-head
machine which simply held the bulb and stem in their
proper relative positions while the two parts were sealed
together. The machine held the work in a horizontal
position, which is the natural position in hand working.
While the machine enabled unskilled operators to perform
the sealing-in operation, it did not increase the number
an operator could produce in a day. The work rotated
while it was being sealed in.

The first of the modern glass working machines was
the four-head vertical seaHng-in machine, made by John
W. Howell in 1S96, and which was essentially the same as
the sealing-in machine of the present day. The work
rotated and was heated in three positions, increasing the
speed of operation very much. With this machine an
unskilled operator could complete 600 lamps a day, which
was more than twice as much as could be done before.
These machines were made just in time to enable the
factory to take care of a large increase in production
without increasing floor space.

''Tipless" Construction

The tip of glass left on the round end of the bulb has
always been recognized as an objectionable feature and
many efforts have been made to get rid of it by tubulating
the glass chamber in a position which would enable the
tip to be covered by the base of the lamp, making a so-
called "tipless" lamp. Many lamps have been made in
previous years which were tubulated in the stem or at
the seal of the bulb and stem, but the methods by which
they were made were expensive and slow.

170

THE INCANDESCENT LAMP

One tipless method of construction was to weld a tube
on the rounded end of the lamp bulb as was done in making
the standard tipped lamp, and weld the glass stem holding
the filament to the bulb. After this weld had been made a
fine pointed flame was allowed to heat the glass at the
seal where the stem is welded to the bulb. When the
glass became soft, air was blown into the tube on the bulb

TUBULATED SEAL
By welding a curved exhaust tube to the seal, the tip on the sealed
exhaust tube would be covered by the base, making a "tipless"
lamp. The construction was too expensive for the general product.

and blew a hole through this soft glass part of the flare.
A piece of curved glass tubing was then welded to this
hole for the subsequent purpose of exhausting the air
from the lamp. The tube on the bulb was then melted off
and the hole closed up by allowing the soft glass to flow

171

THE INCANDESCENT LAMP

together, so that the bulb looked the same as before.
The air was then pumped out through the curved exhaust
tube, which, when sealed off, was covered by the base.

Another method was to make a nick in the edge of the
flare of the glass stem so that when the stem was sealed
in the bulb this nick left a hole in the edge of the seal.
The curved exhaust tube was then welded to this hole in
the flare. This did away with the necessity of welding the
glass tube on the bulb of the lamp and later removing it.

Meridian Lamps

H. D. Burnett and S. E. Doane, of the General
Electric Company, obtained a patent in 1894 for a
tipless construction which, however, was not com-
mercialh^ used until about twelve years later, and
then used only on a special type of lamp called the Meridian
lamp, designed for decorative purposes to compete with
the Nernst lamp. It was possible to obtain a higher
price on the Meridian, lamp, as compared with the standard
line of incandescent lamps, which warranted the expense
of making it tipless.

A machine was developed by Mark H. Branin, of the
General Electric Company, for which he obtained a
patent in 1906, to reduce the amount of handwork
othenvise necessary in making the Meridian lamp. Inside
the stem tube, in which the leading-in wires were
later imbedded, a smaller diameter tube was placed through
which the lamp was later exhausted. The end of the ex-
haust tube toward the inside of the lamp was flared and
rested on a mandrel which projected into the exhaust tube.

The stem tube with the leading-in wires and exhaust
tube were then heated at the end near the mandrel and
when the glass was soft the parts were pinched together
by a pair of pincers, which had a hole in the middle. This
pinched the two glass tubes together so that a pair of glass
"ears" were formed in which the leading-in wires were
imbedded. The mandrel and hole in the pincers prevented
the exhaust tube from collapsing.

172

THE INCANDESCENT LAMP

This process had many difficulties and caused a large
amount of spoilage. The operator had to watch the condi-
tions existing in the machine very closely. If the mandrel
supporting and holding the exhaust tube open during the
pinching process in making the seal became heated too
much the glass would stick to it and be drawn out of
shape when the stem was removed. If the mandrel was

MERIDIAN LAMP, 1906
The exhaust tube was placed inside the stem tube, the two sealed to-
gether at the end. The leading-in wires were imbedded in glass
protuberances made while the two were sealed together.

too cool it was apt to cause cracks in the glass, so that
a considerable percentage of the product was spoiled.
With the advent of the more efficient tungsten lamp the
popularity of the Meridian lamp soon waned, its manufac-
ture being stopped in 1910.

173

THE INCANDESCENT LAMP

Jaeger Tipless Lamp

In 1903, Herman J. Jaeger obtained a patent on a tipless
construction which consisted of an "L" shaped exhaust
tube sealed to the inside of the stem tube away from the
pinched seal. After the stem had been made in the usual
way, this "L" shaped exhaust tube was inserted in the stem
tube and a fine pointed flame heated a spot on the side
of the latter. The bent portion of the exhaust tube was
then welded to this heated spot in the stem tube and by
blowing through the exhaust tube a hole was made through
the stem tube. Thus the exhaust tube, when sealed off.

JAEGER TUBULATED STEM
An ' 'L" shaped exhaust tube was sealed to the inside of the stem tube
away from the pinched seal.

was covered by the base, making a tipless lamp. This lamp
was marketed for a number of years by the Tipless Lamp
Company.

The Stemless Butt Seal

Low volt miniature lamps used as indicators in telephone
switchboards have largely been made tipless since about
1898. In 1913, this construction was applied to flashhght
lamps and, in 1915, to side and rear automobile lamps.
These lamps have no glass stem to support the short fila-
ment, it being supported entirely by the two leading-in wires
held rigidly together by a globule of glass. The leading-in
wires, with the filament, are put inside the bulb, the wires
bent over the edge of the neck of the bulb (which is of
small diameter) and the flared end of a glass exhaust
tube welded to the neck of the bulb, the leading-in
wires being imbedded in the weld. This method of con-

174

THE INCANDESCENT LAMP

structjon was practicable only with the stemless filament
supported by the leading-in wires. The standard lighting
lamps for 110-volt service require an additional filament
support that is too heavy for the leading-m wires to carry.

STEMLESS BUTT SEAL

This construction has been in use for several years on miniature lamps,

producing a tipless lamp.

Mitchell and White Tipless Cojistructio)!

L. E. Mitchell and A. J. White, of the General Elec-
tric Company, invented a method of tubulating the stem
seal which made a great improvement in lamp construc-
tion. Their method eliminated tubulating as a separate
operation, thus reducing the cost of lamp making and
eHminating the exposed tip on the lamp. All lamps for
standard lighting service are now so made.

In this method the exhaust tube is placed inside the
stem tube in the stem making machine. The inner ends
of the two tubes are sealed together, closing both tubes,
making a mass of glass in which the leading-in wires are
imbedded. While this mass of glass is still soft, air is blown
in the outside end of the exhaust tube, the air pressure
blowing a hole through the soft glass at this soft mass.

175

THE INCANDESCENT LAMP

Through this hole the exhaust tube communicates with the
inside of the bulb.

Thus the tubulation of the lamp is done on the stem
making machine. When the lamp has been exhausted
and, in the case of gas-filled lamps, the gas has been allowed

MITCHELL & WHITE TIPLESS CONSTRUCTION
The exhaust tube is put inside the stem tube with the leading-in wires,
the end fused and pinched together. While the seal is still soft,
air is blown through the exhaust tube making an opening at the seaL
All standard lamps are now made this way.

to flow in, the exhaust tube is sealed off close to the lamp
so that the tip is completely concealed by the base.

Frosting

The light from a clear bulb incandescent lamp is
exceedingly dazzling on account of the high brilliancy of
the filament. In a carbon filament lamp this brilliancy is
about a hundred times that of the ordinary candle and in
a tungsten filament lamp from 200 to 2500 times. Thus
while clear bulb lamps should always be shaded, in many

176

THE INCANDESCENT LAMP

cases the bare lamp must be used for various reasons.
Under these circumstances "frosted" lamps have been
occasionally used in place of clear ones, since the bril-
liancy is reduced about a hundred fold by frosting.
Originally, the frosting consisted either of acid etching or of
a coat of mineral paint sprayed onto the surface of the bulb.
The higher cost and slight loss of light due to absorp-
tion by the frosting prevented the use of frosted lamps in
many places where they should have been used. These

»^^

f^

l¥ew« v^ =«aii^\«* "5 •"", /-»«»*> nCMt '^^.-^ * :3^C^ ^ . Mmm^

Before Treat in

i/tcr Ircdlm

PHOTOMICROGRAPHS OF INSIDE FROSTING
If a lamp bulb is acid frosted on the inside, the bulb becomes fragile.
Marvin Pipkin restored the strength by a chemical treatment
which rounded out the minute cracks made by the acid frosting.
Inside frosting absorbs less than two per cent of the light, which is
about one-third that absorbed by outside frosting.

objections, and the limitations they imposed on the frosted
type of lamp, have been eliminated by a recent invention
of Marvin Pipkin of the General Electric Company, which
not only cuts the loss by absorption to a third of its former
value, but, since it is practical for quantity production,
has reduced the price of the lamps.

The advantages of frosting an incandescent lamp on
the inside of the bulb have been realized for many years,
but until recently no satisfactory method has been devised.

177

THE INCANDESCENT LAMP

It is obvious that a lamp having a smooth outer surface,
will be miore apt to stay clean than one having a roughened
outer surface.

The absorption due to frosting is considerably less
with inside than with outside frosting. If the frosting is on
the outside, the light from the filament goes through the
glass wall of the bulb to the irregular frosted surface where
some of it is diffused. The remainder of the light is reflected
back through the glass to the opposite wall of the bulb.
This process is repeated again and again until most of the
Hght gets out. Some light, however, is absorbed each time

STANDARD LAMPS
These are the six standard lamps of the new line which replaced the
forty-five different types and sizes for standard lighting service
previously used. The lamps have a new shaped bulb which is
frosted on the inside.

it passes through the glass. If the frosting is on the inside
surface of the bulb, the cross reflections from the frosting
do not have to pass through the glass walls of the bulb each
time, which may be an explanation for its lesser absorption.
The ordinary acid frosting on the inside of the bulb
weakens the bulb and renders such lamps subject to break-
age. It etches the bulb and causes minute cracks or splits
to appear just below the surface of the glass. When the bulb
is evacuated, the inside surface of the glass is under tension
from the air pressure on the outside surface, and the cracks

178

THE INCANDESCENT LAMP

on the inside surface of the bulb cause it to break easily
just as a steel truss will break with a crack at the bottom and
pressure on top. If the frosting is on the outside, the glass
is not materially weakened, as then the etched glass surface is
on the outside under compression, the compressive strength
of a piece of glass being greater than its tensile strength.

It is a well known fact that if a round hole is drilled
at the end of a crack or split in a steel truss, it will withstand
a greater weight. Mr. Pipkin discovered that if an inside
frosted lamp is subjected to the proper treatment, the
entire area of the inside surface will become etched in
such a manner as to round out the bottoms of these cracks.
The effect of this action is to restore the strength of the bulb
to its former value. This he accomplished by chemically
treating the inside of the bulb after it had been acid etched.

The new inside frosted lamps were first put on the
market in 1925 with a new shape of bulb which is considered
more pleasing in appearance and which is expected to
replace many of the different shaped bulbs used in the past.
This new standard line of six lamps is intended to replace
approximately forty-five different lamps heretofore supplied.

The Unit Machine

The process of making a lamp consists of a succession
of steps, each of which is an independent operation. A
glass tube is made into a stem, a glass rod welded to it and
little wire supports set into it to hold the filament. The
filament is draped on anchors and pinched fast to the
ends of the leading-in wires. The stem with its filament
is inserted in the bulb and the stem and bulb are fused
together. The air is exhausted and gas inserted if it is
to be a gas-filled lamp. The base is cemented on. The
leading-in wires are soldered to the base. The lamp is
tested, wrapped and packed in a carton and then in a case.
It is one long succession of delicate little operations.

One of the difficulties has been the problem of main-
taining a balance in the quantity of the different parts
manufactured. This has led to the necessit}^ for storage

179

THE INCANDESCENT LAMP

of parts between operations. It has required a great deal
of floor space and an expenditure for labor in handling
and rehandling materials. Various individual machines
used in the different operations ran at their own particular
speed of efficiency and the effort was to keep a balance
amongst the number of machines or operators in each
department that would maintain a uniform production.

UNIT MACHINE

In this machine, having four operators making standard lighting lamps,
the heretofore individual processes in lamp making are co-ordinated.
The result has been that the floor capacity of lamp factories has been
tripled and the output per operator doubled.

Soon after the close of the war, when industrial men
began to turn their thoughts once more to plant improve-
ments, W. R. Burrows began to see the possibilities for
correlating the machine steps in the manufacture of a
lamp. His first move was to take one of the various ma-
chines out of each department and set them up side by
side to work in sequence with each other and with the

180

THE INCANDESCENT LAMP

different hand operations required. There gradually
developed the conception of balancing these machines
and the hand work processes so that materials would flow
evenly into the unit of machines and all storage of parts
between operations might be eliminated.

By gradual evolution, the result of endless experiment
and a tremendous amount of machine development, this
very end was accomplished. Out of it finally came a
unit lamp-making machine, one single combined mechanism
into which glass bulbs, tubes and rods, filament wire,
anchor wire, bases and packing materials are fed. Out
of the other end come finished lamps, marked, tested,
wrapped, packed and laid in a case upon a conveyor belt
that carries them away to be shipped.

In the present unit machine there are three to seven
operators, depending on the type of lamp, turning out
twice as many lam.ps per operator as were made by the
old departmental method. It is expected that machines
will soon be available requiring a lesser number of operators,
perhaps as low as two, in which much of the hand work
now done will be made automatic. Another great advan-
tage of the unit machine is that it has tripled the capacity
for a given floor space, because it has eliminated the
storage of parts between operations.

These advantages have materially reduced the cost of
manufacture, making possible a reduction in prices. At the
present time the price of lamps is more than one-third
below the pre-war level, an accomplishment which few
industries can claim and which is even more remarkable
when it is considered that the present average price of
commodities is over 50 per cent above their pre-war figure.

Another interesting thing about the unit machine is
that the quality of lamps has improved through its use.
This is due to the ability to locate definitely imperfect
manufacture in any given part of the lamp which was almost
impossible to fix by the old departmental method where
the part may have been made in any one of a great many
individual machines.

181

CHAPTER SEVEN
The Base

In the latter part of 1879, when Edison had invented
a practical incandescent lamp, it was apparent that a
device must be made whereby the lamp could be readily
connected to the circuit. The first attempt at such a device
consisted of wooden stand having two ordinary binding
posts. As this required fastening the circuit wires to the
binding posts each time the lamps were replaced, the
danger of making a short circuit with the loose wires soon
indicated the need for a socket and a base to fit into it.

ORIGINAL LAMP BASE. 1879
This was before a socket had been invented, the circuit wires being at-
tached to the binding posts on the wooden stand holding the bulb.

The first socket consisted of a hollow piece of wood
containing two strips of copper, fastened at one end inside
the wood on opposite sides of the socket. A thumb screw
forced the two strips to make a rigid contact between two
similar copper strips fastened to the neck of the bulb. One
end of each of the copper strips on the lamp was soldered

182

THE INCANDESCENT LAMP

to the corresponding end of the leading-in wire and the
other end was held against the neck of the bulb b}^ wrapping
string around it.

- 1 I

VJIRE TERMINAL BASE. 1880
Copper strips were fastened to the end of the leading-in wires, the ends
of the strips being secured to the neck of the bulb by string.

ORIGINAL SOCKET, 1880
This consisted cf a hollow piece of wood containing two strips of copper.
A thumb screw forced the two strips to make a rigid contact with
the copper strips on the neck of the lamp, when the lamp was in-
serted in the socket.

This first base was superseded in the latter part of
1880 by a screw base. It consisted of a screw shell for one
terminal and a ring for the other terminal. Wood was

183

THE INCANDESCENT LAMP

used to insulate and hold together the parts of the base.
The base was cemented to the neck of the bulb by plaster
of pan's. This base was large and bulky and was soon

ORIGINAL SCREW BASE. 1S80
This was the first screw base. It consisted of a screw shell and a ring
for terminals with wood for insulation. It was fastened to the
bulb by plaster of paris and was a bulky affair.

ORIGINAL SCREW SOCKET, 1880

This was made of wood, the copper terminals inside being designed

to accommodate the original screw base pictured above.

changed, early in ISSl, to a smaller sized base having a
cone-shaped ring and screw shell for terminals. Soon

184

THE INCANDESCENT LAMP

afterward the use of wood for insulation was abandoned,
plaster of paris being used instead, both for insulation and to
hold the two parts of the base together and to the bulb. It
was found, however, that when the lamp was firmly screwed
into the socket, the pressure of the cone-shaped ring
terminal of the socket against the similar terminal of the

IMPROVED SCREW BASE. 1881
The terminals of this smaller base were a cone shaped ring and a screw
shell with wood insulation.

PLASTER SCREW BASE, 1881

To simplify matters, the wood insulation was omitted, plaster of paris

being used for this purpose as well as for fastening to the bulb.

base produced a tension on the plaster of paris between the
two terminals of the base so that it was liable to be pulled
apart.

A few months later, about the middle of 1881, this
difficulty was overcome by changing the base terminals
to a screw shell and an end contact so that by screwing
the base in the new socket, changed of course to fit the
base, pressure instead of tension was put on the plaster of

185

THE INCANDESCENT LAMP

FINAL SCREW BASE. 1881
In the previous base, it was found that when the lamp was firmly
screwed in the socket a tension was produced on the plaster in-
sulation between the two terminals so that the base was apt to be
pulled apart. This was overcome by changing the terminals to a
screw shell and an end contact, as illustrated, producing a pressure
instead of tension on the plaster insulation. This arrangement has
been used ever since, and this base will fit present day sockets.

/

I

EDISOX LAMP. 1884

The ring of plaster about the neck

of the bulb, heretofore used as

handle, was omitted in 1884.

EDISOX LAMP. 1888

The length of the base was increased

in 1888 so that it had more

threads.

1S6

THE INCANDESCENT LAMP

paris insulation. This arrangement of the terminals for
the base is the same as is standard today. While sHght
dimensional modifications have since been made, this
base will fit present day sockets. This screw base, gener-
ally known throughout the electrical industry as the
Edison base in honor of its inventor, has become the world

BASIN'G RACK
This was used in basing lamps when plaster of paris was used.

wide standard and lamps fitted with it are annually made
throughout the world in quantities many times greater
than the combined quantity of lamps fitted with all other
bases.

The base had a ring of plaster about the neck of the
bulb for use as a handle to screw the lamp into the socket.

187

THE INCANDESCENT LAMP

In 1884, this ring of plaster was omitted. In 1888, the
length of the screw shell was increased, more threads
being put on. Owing to the fact that the necks of the
free blown bulbs used were not of uniform size, various
lengths of screw shells had to be used to fit the various
lengths of bulb necks. With the adoption of the moulded
bulb, this requirement was no longer necessary.

The method of attaching the base to the lamp was to
put the two terminals in a mould mounted on a rack,
pour plaster of paris in the mould, thread one leading-in

iifiyv

EDISON LAMP, 1900

Moulded porcelain was used for insulation in the base which was fastened

to the bulb with a waterproof cement in place of plaster of paris.

wire through the hole in the end contact terminal, bend
the other leading-in wire back on the neck of the lamp and
insert the neck of the lamp in the mould. Guides on the
rack were lowered over the tip of the lamp, to align the
lamp and base properly, and the plaster allowed to dry.
The plaster of paris became fairly hard in about twenty
minutes, when the mould was removed and the lamp with
its base put in a heated enclosure to drive out the

188

THE INCANDESCENT LAMP

moisture from the plaster, a process requiring about 36
hours. The excess length of the leading-in wires was then
cut off, their ends being soldered to the base.

Waterproof Base

The plaster of paris would absorb moisture when the
lamp was used in exposed places, such as in outdoor signs.
In 1900, porcelain insulation was used to hold the parts of
the base together, the base being fastened to the bulb by
a waterproof cement. This cement consisted of plaster

EDISON LAMP. 1901

Glass was used in the base for insulation in place of porcelain. This is

the same as used today.

of paris with a shellac solution which, when heated, made
a hard waterproof cement through the evaporation of the
alcohol in the shellac. The tensile strength of the cement
was later improved by substituting Portland cement, or in
some cases marble dust, for the plaster of paris. Bakelite
is now used and, in order to determine whether or not it is
heated to the proper temperature, a green dA^e is mixed
with the powdered bakelite, the dye decomposing at a
certain temperature so that the green color disappears.

189

THE INCANDESCENT LAMP

I h. TM.n Houston Westiiighousc. Brusri-.^wai

Schaeffer or Xatifi

t

l'"di-S\van Eili-Swan

(single contact I. ulonl.le contact

Hawkeve.

Sicnreii5 & Habk

SOME OF THE VARIOUS BASES IX USE PRIOR TO 1900
A fewof these had disappeared from use, the proportion in 1900 being
70 per cent Edison, 15 per cent Wcstinghouse, 10 per cent Thomson-
Houston, and 5 per cent for the others remaining.

190

THE INCANDESCENT LAMP

In 1901, glass was usedto insulate and hold the terminals
of the base, this being made possible by an invention by
Alfred Swan, of the General Electric Company. This
greatly reduced the cost of the base, and all bases are now
so made. A fine stream of molten glass is allowed to flow
in a holder containing the screw shell and the end contact.
When a sufficient amount of niolten glass has been put in, a
jet of air blows the stream of glass to one side — it cannot be

Thomson-Houston Westinghouse

ADAPTERS FOR EDISON BASE LAMPS

The adapter placed in the socket permitted the use of lamps fitted with

Edison base.

shut off as it would otherwise freeze up in the orifice — and
a plunger is inserted which shapes the glass, leaving a hole
through which the leading-in wire can be inserted and
soldered to the end of the base.

Other Bases

Soon after the commercial introduction of Edison's
lamp, many other concerns began making lamps, each with
an individual design of base. This required a correspond-
ing socket to fit the base and no less than fourteen different
designs were in use at one time or another.

In 1900, the more important designs in use were the
Edison, which covered about 70 per cent of the total, the

191

THE IKXANDESCExXT LAMP

Westinghouse, 15 per cent and the Thomson-Houston 10,
per cent. The remaining 5 per cent covered the other designs.

Standardizing the Edison Base

As the use of incandescent lamps became more general
and the necessity arose for more types of lamps to meet
individual specific requirements, together with the need
of stocks at convenient distributing points throughout
the country to supply the demand promptly, the existence
of so many dift'erent lamp bases presented a situation
which, if continued, would seriously retard the develop-
ment of the electric lighting industry. The necessity
for overcoming this condition seemed imperative and it
was recognized that something must be done to simplify
the lamp base problems.

The task seemed insurmountable. At this time, 1900,
there was an aggregate of about fifty million sockets of
various designs in use in the United States. It seemed
desirable to standardize on the Edison base and socket
because of the simplicity of its design and extent of its use.
To change the sockets of the types other than Thomson-
Houston and Westinghouse to the Edison type of socket
was considered possible, but to replace every Thomson-
Houston and Westinghouse socket with an Edison screw
socket was thought impossible. It appeared, however, that
adapters could be designed to enable existing Thomson-
Houston and Westinghouse sockets to receive lamps fitted
with the Edison screw base, but even this was considered
by many to be impossible of accomplishment commercially.
Nevertheless, believing that it should at least be tried, the
adapters were designed and made, being sold at cost.

The campaign, which was started to effect the cor-
responding changes commercially, was so successful that
in less than five years the demand for lamps in the United
States with other than the Edison base practically ceased.
At the present time, the five hundred million sockets
now in use in this country on commercial lighting circuits
are all of the Edison screw type.

192

CHAPTER EIGHT
Photometry

The incandescent electric lamp is responsible for the
great development which has taken place in the art of
photometry. Before Edison invented his lamp, photom-
etry was a crude art and was little used. Laboratories
and some gas plants had photometers, using as standards
of light either candles or oil lamps, both of which were so
variable that there were no really dependable standards.
Even though the law in some states specified that a gas
burner which consumed five cubic feet an hour, should
give sixteen candle power, some gas companies that had
photometers rarely used them.

The method then in use was to burn two standard
candles at one end of the photometer as a standard of
light. These candles were set in a balance which weighed
the consumption of material per minute while the measure-
ments were being made, and measurements were then cor-
rected for variations from the specified rate of consumption
of the candles. The hght given by these candles varied
with other conditions, such as the length of the wick, for
example, but it was a rule not to trim the wicks during the
measurements. In fact the public was not much con-
cerned with candle power at that time.

When incandescent electric lamps came into use,
their candle power and efficiency at once became matters of
great importance and interest. Edison claimed to get
eight 16-candle power lamps per horse power of electricity
and constant tests were made to see that the lamps made
each day met this condition. Candles were used as the
standards of light, but their daily use in the photometers
was soon superseded by carefully standardized incandescent
lamps. These standard lamps burned as long as the pho-
tometer was in use, which was usually all day, and were

193

THE INCANDESCENT LAMP

frequently checked and corrected by comparison with a
number of other carefully prepared lamps used only for
this purpose. This method of photometry originated in the
laboratory at Menlo Park and has been the universal
method ever since.

Every lamp made was measured to determine the volt-
age at which it gave 16 candle power. This voltage was
measured by means of a reflecting electro-dynamometer

STANDARD PHOTOMETER
This measures the mean horizontal candle power of lamps. At the
right, the standard lamp is set, against which the lamp to bephoto-
metered (on the left) is balanced. The voltage and current taken
by the lamp being photometered is measured at the same time.

made for the purpose. The scale read to 150 volts and
each volt near the hundred volt mark gave a deflection of
about three-sixteenths of an inch on the scale. The
measurements were made on a circuit of 150 volts, resistance
being put in series with the lamp to reduce the line voltage
to that required on the lamp, which was measured by the
electro-dynamometer. The voltage of the line was held
constant at 150 volts by manual regulation.

194

THE INCANDESCENT LAMP

There were no ammeters at that time. The resistance
in series with the lamp when it was being measured was in
steps of one ohm each. The voltage on the lamp was read
on the electro dynamometer and the resistance in series
with the lamp was noted. The difference between 150 volts
and the voltage on the lamp was the voltage on the variable
resistance and this voltage divided by the resistance noted
was the current passing through the lamp. All lamps at
that time were measured at 16 candles and curves drawn
on cross section paper made it possible to determine the
candles per horse power which the lamp gave with the
known voltage on the lamp and the resistance in series
with it on the 150- volt circuit.

Each lamp, being rated to consume one -eighth of an
electrical horse power, was therefore designed for 9334
watts (one-eighth of 746). The correctness of the power
measurements was checked by burning a lamp in a calo-
rimeter and measuring the rise in temperature of the water
during a measured time. The calorimeter method was
well worked out in its details and gave quite good results.
This method of measuring lamp efficiencies continued
until about 1890, when reliable voltmeters and ammeters
were developed by Edward Weston. It was not necessary
to measure the efficiency of every lamp made, but it was
necessary to photometer every lamp manufactured to
determine the voltage at which it gave its rated candle
power.

The first test department was established at the
laboratory in Menlo Park, in 1880. In March, 1881,
a much more complete test department was set up in
the Lamp Factory at Menlo Park by Dr. Edward L. Nichols.
In April, 1882, the Lamp Works moved to Harrison and
with it the test department. In 1887, the test department
was moved to Edison's new laboratory at Orange, N. J.,
and in 1893 it was moved back to Harrison.

About 1886 J. T. Marshall, of the General Electric Com-
pany, invented a method of determining the voltage at which
a lamp gives its rated candle power without requiring the

195

THE INCANDESCENT LAMP

use of any electrical measuring instrument . At one end of
a photometer he placed a seasoned lamp of the type to
be measured on the photometer and of a known voltage,
which was the voltage for which the lamps to be meas-
ured were designed. The lamp to be measured was placed
at the other end of the photometer and the two were con-
nected in multiple so that both had the same voltage acting
on them. If the lamp being measured was of the same

SLIDING SCALE PHOTOMETER
In this photometer lamps were measured for their voltage to give their
rated candle power without the use of electrical measuring instru-
ments. An empirical scale attached to the balancing screen (in the
center) gave the voltage.

voltage as the standard lamp, they would both give the
same candle power and the photometer spot would balance
in the center of the scale, this point being marked as the
voltage of the standard lamp. If the two lamps differed
in voltage, they would also differ in candle power and the
balancing position of the spot would indicate the voltage
of the lamp being measured, by means of an empirical
scale.

196

THE INCANDESCENT LAMP

Voltage fluctuations on the line did not affect the re-
sults in this method as the two lamps varied similarly, so
this photometry was done on a line which was not care-
fully regulated. This method allowed very fast operation and
was a great boon to photometer work. This "sliding scale"
or "same circuit" photometer was in regular use until
the advent of the drawn tungsten wire lamp in 1911, when
it was no longer necessary to photometer each drawn
tungsten wire lamp. Every carbon, Gem, tantalum and
pressed filament tungsten lamp had to be photometered
individually to determine its voltage.

The reason why it was not necessary to photometer
drawn tungsten wire lamps was that the filament could be
made to such an exact diameter and length that each lamp
could be manufactured to extreme closeness of candle
power and efficiency. Sample lamps were photometered
to check the manufacture, and the lamps usually came
out so close to their designed rating that if the photo-
metric measurements were found to differ from the de-
signed rating, the chances were that there was an error
in the photometric readings.

Carbon lamps were all measured for mean horizontal
candle power, because they varied in candle power in dif-
ferent parts of the horizontal plane. It was the practice at
first to select an average position and measure the lamps
in this position. Later the lamps were rotated about their
vertical axis while being measured in the photometer,
their average horizontal candle power being obtained in
this way.

The relation of the horizontal candle power of each type
of lamp to its spherical candle power was known. The
spherical candle power is the average candle power in all
directions. The relation between the two, known as the
reduction factor, was 0.825 for the oval anchored carbon
lamp, so that its spherical candle power could be deter-
mined by taking 823^2 P^i* cent of its horizontal candle
power measurement.

197

THE INCANDESCENT LAMP

When tungsten filament lamps were developed in many
forms of filament shapes, their ratios of horizontal to
spherical candle power varied a great deal. It therefore
became advisable to change all ratings to the basis of
spherical candle power, which eventually became standard
practice. The spherical candle power can readily be meas-
ured by burning the lamp in a hollow sphere which has a
matt- white inside surface. The cross reflections inside

SPHERICAL PHOTOMETER
With this photometer the spherical candle power of a lamp, the aver-
age candle power it gives in all directions, can be obtained by but
one measurement.

the sphere, coming from the light thrown out in all
directions by the lamp being measured, fall on a diffusing
glass test piate located on the periphery of the sphere,
the direct light from the lamp being screened from the test
plate. The Hght from the test plate is balanced by a
standard lamp and therefore gives, in one reading, the
spherical candle power of the lamp being measured.

198

THE INCANDESCENT LAMP

In the early days the efficiency of lamps was measured
in candles per horse power. Later the name watt was
given to the unit of electric power and after that lamp
efficiencies were stated in watts per candle. The candle
in both cases was the horizontal candle power. With the
measurement of lamps in spherical candle power, the lamp
efficiency was stated in watts per spherical candle. The
two terms, watts per candle (wpc) and watts per spherical
candle (wpsc), often led to confusion, so that efficiency
came to be designated by the term lumens per watt (lpw).
This term lpw has an advantage in that the higher the
efficiency, the higher the lpw becomes numerically,
whereas the reverse obtains with the terms wpc and wpsc.

The lumen is the unit of light flux, and the efficiency of
all lamps is now measured in lpw. The lumens delivered
by any lamp are 12.57 times its spherical candle power.
A lumen is the light flux which a point source of one candle
power of light will throw upon a surface of one square
foot, every point of which is located one foot distant from
the point light source. So if a light source of one spheri-
cal candle is placed at the center of a sphere of one foot
radius, it will yield as many lumens as there are square feet
on the inside surface of this sphere, or 12.57 lumens.

In all photometric work, the light of the lamp under
test is compared with the light given b}' a working standard
lamp, the correctness of this working standard lamp being
frequently determined by comparing its light with that
given by a number of photometric standard lamps kept for
the purpose. Hitherto all practical photometric measure-
ments have been made by a visual comparison of the
lamp to be measured with the standard lamp and, there-
fore, have depended on the judgment of the eye.

Photometry is not the measurement of an external or
objective dimension, but of a sensation, and it is difficult
to make a quantitative measurement of our sensations.
The attempt to apply measurement to the sensation of
smell has not met with success. In spite of the delicacy
with which different sensations of taste may be discrimi-

199

THE INCANDESCENT LAMP

nated, it has been impossible to measure taste, particularly
as there seem to be physiological reasons for a rapid
approach to a saturated condition of the sensation. A
similar difficulty arises in the action of light on the eye.

Many attempts have been made to develop a practical
method of photometry which did not depend for its
accuracy on the human element. Among them may be
mentioned the Thermopile, and the Bolometer, which have
both been used to measure the whole radiant energy given
out by a lamp. This was done by means of electrical appa-
ratus, the dark heat rays being filtered out from the lumin-
ous rays by a process of selection. The proportion of energy
in the luminous rays is so small compared with the thermal
or heat energy rays that it has been impossible to arrive at
any precise measurement of light alone. The electrical
properties of selenium have given some promise of a quan-
titative indication of the intensity of light. Photographic
methods have been stiggested and tried by exposing strips
of sensitized paper for a definite time and comparing them
with the shades obtained from known illuminations.
None of these schemes has been able to compete in a prac-
tical way with an ordinary visual photometer.

Recently, however, Charles Deshler, of the General
Electric Company, has developed a photometer which
substitutes a " mechanical" eye for the human eye. The
comparison of light sources, the photometer spot and the
working standard lamp have been entirely eliminated. The
lamp whose lumens are to be measured is placed as usual
in the sphere of a spherical photometer. The integrated
light of the lamp passes through a suitable color filter, or
test plate and filter, and impinges on a photo-electric cell.
A suitable potential is placed across the cell, and the cur-
rent flowing under these circumstances is proportional to
the lumens given by the lamp. This current is measured
by a microammeter or galvanometer which thus becomes a
"lumen-meter". The photometer is extremely accurate,
eliminates the varying human element of the eye, and is
much more rapid than any visual photometer.

200

THE INCANDESCENT LAMP

The principle of the photo-electric cell is based on an
electrical property of alkali metals when subjected to light.
When the surface of such alkali metals as potassium,
barium, strontium, sodium, etc., is exposed to light, it
liberates electrons like the heated filament in a radio tube.
The cell usually consists of a glass bulb with two terminals.
One, the positive terminal, is at the center of the bulb and

PHOTO-ELECTRIC CELL
This consists of a glass bulb, coated on the inside with an alkali metal
compound, which emits electrons when subjected to light, so that
the strength of the current flowing from this coating to a positively
charged terminal in the bulb is a measure of the candle power of the
light.

is equivalent to the plate of a radio tube. The other, the
negative terminal, consists of an alkali metal film deposited
on the inner surface of the bulb, and is equivalent to the
filament in a radio tube. This metal film covers the entire
inner surface of the glass bulb except for one clear spot,
called the "window," through which the light to be meas-
sured can enter the interior of the bulb. When an electrical

201

THE INCANDESCENT LAMP

circuit outside the cell is established through a battery,
with the positive of the battery connected to the center
(positive) terminal and the negative battery terminal con-
nected through a galvanometer to the metal film (negative)
terminal of the cell, the electrons emitted from the metal
film will be attracted to the positive terminal inside the bulb,
as in a radio tube, and then will flow through the outside
circuit back to the negative metal film.

SPHERICAL PHOTOMETER WITH PHOTO-ELECTRIC
CELLS
The light from the lamp to be photometered falls on the photo-electric
cells mounted on the outside equator of the sphere. The current
flowing through the cells passes through a galvanometer which de-
flects a ray of light on a scale and thus indicates the candle power of
the lamp being photometered.

This flow of electrons is the modern theory of the flow
of electric current, and as the number of electrons emitted
by the metal film depends upon the intensity of the light
thrown on it, the strength of the electric current in the
outside circuit becomes a measure of the intensity of the

202

THE INCANDESCENT LAMP

light. While this current is minute, of the order of a few
millionths of an ampere, it can be measured by a micro-
am.meter or by the deflection of a galvanometer needle.

Potassium hydride, an alkali metal compound, is now
generally used as the metal film on account of its rela-
tively high melting point and sensitivity. The bulb is
highly evacuated and filled to low pressure with an inert
gas such as argon, helium, etc. The introduction of these
gases produces ionization by collision of the electrons with
the molecules of gas in the bulb so that a given intensity
of light thereby greatly increases the strength of the current
through the cell.

There are two essential difficulties which had to be
overcome before the cell could be used satisfactorily for
photometric purposes. The first is color sensitivity; that is,
the cell responds to certain colors of the spectrum to a
greater extent than does the human eye. This was
the main difficulty which previously precluded the use ot
the cell, but it was overcome by the use of a color
filter of the proper color. Lamps of equal candle
power to the human eye, but which are different in
efficiency, have different proportions of the various colors
making up the light which they give and so the cell,
without a proper filter, would indicate different
candle powers. This would mean that, for example, a 100-
watt Mazda C lamp, which is about twice as efficient as a
10-watt Mazda B lamp, but whose light is much whiter
than that of the latter, would be indicated by the cell
as giving more than twenty times the difference in candle
power between the two lamps as seen by the human eye.

The second difficulty, the minuteness of the current,
has been overcome by using a high sensitivity galvan-
ometer or microammeter. With lamps of very low candle
power more than one cell can, if necessary, be used in mul-
tiple to increase the amount of current.

Life Testing

After the invention of the lamp by Edison, two
great questions had to be answered: how much power is

203

THE INCANDESCENT LAMP

required to operate the lamp and how long will the lamp
last? In those days the power required to operate a lamp
was expressed by the number of candles produced per
horse power of electricity consumed. It was immediately
observed that the candles per horse power became greater

LIFE TEST RACKS.

This photograph shows part of the equipment used in life testing

lamps at the Edison Lamp Works.

as the temperature of the filament was raised, and it was
also observed that as the temperature was raised the life
of the filament became shorter. Edison concluded that
a lamp to be satisfactory must last about 600 hours,
and tests were started to determine the candles per horse
power at which the lamps would last 600 hours — so a life
test department was created in 1880 at the laboratory at
Menlo Park. Early in 1881, a much better one was set
up in the Lamp Factory at Menlo Park.

204

THE INCANDESCENT LAMP

The life test department made it possible to rate
lamps as improvements were made so that they would last
600 hours, and to determine the worth of experimental
lamps, so its importance and value were recognized from
the beginning. Life testing lamps at their normal rating
took a long time, so, as early as 1880, tests at higher than
normal rating were regularly made. Lamps were life tested
at three times their normal candle power, 16-candle lamps
being tested at 48 candles. As lamps improved in quality,
this was changed to 64 candles and then to 80 candles.

For this testing a special generator was used, which was
held at 150 volts, being regulated by hand. A resistance
was placed in circuit with each lamp, which could be ad-
justed in steps of one ohm up to 100 ohms, so that any
lamp could be burned at practically any desired voltage
up to 150 volts. From the results of these tests of lamps,
J. W. Howell determined in 1885 the relative lives of lamps
at different initial candle powers. He found that the lives of
lamps varied inversely as the 3.65ths power of their initial
candle power. This exponent has been redetermined and
checked several times since then by different people. Later,
lamps were tested, not at fixed candle powers, but at fixed
watts per candle, and recently at lumens per watt, this be-
ing now accepted as the measure of the efficiency of lamps.

The necessity of life testing is just as great now as it was
in the early days. Samples from the regular production of
every factory are frequently and regularly tested to keep
the makers informed of the quality of lamps made, and
many experimental lamps from the development and
research laboratories are constantly being life tested as an
ultimate test to determine their success or value. Lamps
are also tested for filament strength, brittleness, ductility,
sagging, etc., and each test necessitates the destruction of
the lamps tested in order to determine their ultimate
characteristics. These tests have to be made with the
greatest accuracy and care, the maintenance of the life
test department costing a great deal of money and its work
destroying a great many lamps.

205

INDEX

PAGE

Ampere, A. M 13

Andrus, M 46

Bases 182

Batchelor, C 46

Batteries 11

Bergman & Co 67

Boehm, L. K 46

Bradley, J 64

Branin, M. H 172

Brauner, J. C 76

Bulbs 163

Burnett, H. D 172

Burrows, W. R. . 166, 169, 180

Carbonizing 56, 75

Carman, G. E 46

Clamps 77, 156

Columbia, S. S 61

Coolidge, Dr. W. D 101

Cunningham, D 46

Dean, G 46

Deshler, C 200

Doane, S. E 172

Dumet 160

Dyer, P. S 64

Dynamos : 16

Alliance 22

Alteneck 25

Brett 19

Clarke 18

Edison 51, 69

Faraday 16

Gramme 23

Hjorth 21

Nollet 22

Pixii 17

Pulvermacher 20

Siemens 21, 24

Sinstenden 20

PAGE

Wheatstone 19, 22

Woolrich 19

Edison Elec. Illg. Co. of N. Y. 71

Edison Elec. Lt. Co 48, 58

Edison Lamp Co 64

Edison Machine Works 67

Edison, T. A 46, 115, 148

Efficiency of Lamps. . .83, 199
Electric Tube Co 68

Farmer, M. G 34, 41

Filaments : 75

Coolidge, drawntungsten 101
Edison, Carbon. . .56, 61, 75
Just & Hanaman, Tung-
sten 94

Pacz, Non-sag Tungsten 119

Powell, Cellulose 81

Swan, Parchmentized. . . .37
Von Bolton, Tantalum. . .90

Welsbach, Osmium 88

Whitney, Gem 84

Fink, Dr. C. G 13 4, 160

Flammer, C 46

Force, M. N 46

Friederich, E 136

Frosting 176

Fuse 66

Gas-filled Tungsten Lamp. 137

Gem Lamp 84

General Electric Co 41, 49

Getters 127

Gill, F. W 136

Glass 163

Griffin, S. L 46

Haid, Dr. A 46

Hammer, Maj. W. J.48, 53, 64
Hanaman, F 94

206

INDEX (Cont'd)

PAGE

Hannington, C. F 77

Herald, N. Y 58

Hinds Ketcham & Co 63

Holzer, W 168

Houston, E. J 41

Howell, J. W. 80, 166, 170

Incandescent Lamp Inventors

Bottome 93

Bouliguine 40

Davy 16, 25

DeChangy 33

De LaRue 25

DeLodyguine 9 4

DeMoleyn 27

Edison.... 48, 53, 57, 60, 65

Farmer 34, 42

Grove 26

Just & Hanaman 94

Konn 39

Kosloff 39

Langmuir 137

Lodyguine 38

Maxim 43

Roberts 32

Sawyer 42

Shepard 32

Staite 30

Starr 28

Swan 34

Von Bolton 90

Whitney 84

Jaeger, H. J 174

Jehl, F 46, 57

Just, A 94

Kelly, J. F 46

Kuzel, Dr. H 99

Langmuir, Dr. 1 137

Lawson, J. W 46

Leading-in Wires 159

Logan, T 46

Lumens-per-watt 83, 199

PAGE

Malignani, A 126

Man, A 43, 79

Marshall, J. T 128, 195

Mazda 100

McGowan, F 77

McLaughlin, Maj. F 46

Menlo Park 45, 60

Meridian Lamp 172

Metallized Carbon Filament84
Meter, Edison Chemical. . .68

Mitchell, L. E 175

Moore, W. H 77

Needham, H. H 134

New York Edison Co 71

Nichols. Dr. E.L 195

Novak Lamp 127, 150

Ohm, G. S 14

Osmium Lamp 88

Ott, J. F 46

Pacz, Dr. A 121

Pearl Street Station 70

Photo-electric Cell 201

Photometry 193

Pipkin, M 177

Powell, L. S 81

Randolph, J. F 46

Ricalton, J 76

Sawyer-Man Elec. Co 43

Sawyer, W. E 42, 79, 149

Sealing-in 169

Seymour, J 46

Skaupy, F 132

Sprengel Mercury Pump 35, 123

Stem 156, 165

Swan, A 191

Swan, Sir J, W 34, 82

Swanson, A 46

Tantalum, Lamp 90

Thomson-Houston Co.. 41, 166

Thomson, Prof. E 41

Thoria 119

207

INDEX (Cont'd)

PAGE PAGE

Three- wire System 72 Volta. A 11

Tipless Lamp 170 Von Bolton, Dr. W 90, 99

Treating Process 79 Von Welsbach, Dr. C. A 88

Tubulating 168

Tungsten Lamp 94 Wallace, W 41

Wardlaw, F. A 47

Unit Machine 179 Waring, J 127

Upton F R 46, 64 Westinghouse Lamp Co. 44, 94

' ■ Weston, E 41, 195

Vacuum 123 White, A. J 175

Van Keuren, W. L 161 Whitney, Dr. W. R 84

208

7Q on

DATE

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